# Posts by Reiny

Total # Posts: 38,074

**math**

sum = 1/2 + (1/3+2/3) + (1/4+2/4+3/4) + (1/5+2/5+3/5+4/5) + ... (1/9+2/9+... +8/9) = 1/2 + 3/3 + 7/4 + 10/5 + ... 36/9 = 1/2 + 1 + 3/2 + 2 + ... + 4 looks like an arithmetic series with a = 1/2, d = 1/2, and n = 8 sum = (8/2)(2(1/2) + 7(1/2)) = 4( 1 + 7/2) = 4 + 14 = 18

*February 23, 2017*

**Calculus**

so you know: height = -16t^2 + 160t + 0 , zero, since we started at ground level This is a downwards opening parabola, so it has a maximum at its vertex. What method have you learned to find the vertex, there are several ways. simplest way in this case: find the x-intercepts, ...

*February 23, 2017*

**Math**

No equation to solve. you probably meant "evaluate" the expression. (2^8?5^?5?19^0)^?2?(5^-2/ 2^3)^4?2^28 = ( (2^8)(5^-5)(1) )^-2 * ( (5^-2)(2^-3) )^4 * 2^28 = 2^-16 * 5^10 * 5^-8 * 2^-12 * 2^28 = 2^0 * 5^2 = 25 check my arithmetic

*February 22, 2017*

**math**

secA = 12/5 then cosA = 5/12 = .41666... use your calculator, make sure you either have it set in degrees or radians, depending on what you want. let me know what you got.

*February 22, 2017*

**Math**

http://www.wolframalpha.com/input/?i=plot+y%3D-2x+,+-x%5E2

*February 22, 2017*

**Math/Calculus**

For this type of problem , the first thing you should do is to make sure that the given point actually lies on the curve, or else whatever we do would be just gibberish. I did this, and both points satisfy their matching equation. So, we take the derivative, plug in the point ...

*February 22, 2017*

**Calculus**

using: f(x)?f(xo)+f?(xo)(x?xo) <-- should be in your text 1° = 1° - 0° so let xo = 0, then x = 1 we have : f(x) = sinx f'(x) = cosx since we are using Calculus on trig, our x must be in radians 1° = ?/180 f(1°) = sin0 + cos(0)(?/180-0) = 0 + (1)(?/...

*February 22, 2017*

**precalculus, complex numbers**

can 't read it, don't use codes, they don't work here

*February 22, 2017*

**Math Derivatives**

product rule f'(x) = xcos(?/x)(-?/x^2) + sin(?/x) = (-?/x)cos(?/x) + sin((?/x) f''(x) = (-?/x)(-sin(?/x))(-?/x^2) - (?/x^2)(cos(?/x)) + cos(?/x)(-?/x^2) simplify if needed

*February 22, 2017*

**Math - Related Rates**

V = (4/3)? r^3 when V = 36? 36? = (4/3)? r^3 27 = r^3 r = 3 m dV/dt = 4? r^2 dr/dt 2 = 4? (9)dr/dt dr/dt = 2/(36?) m/min = appr .01768 m/min

*February 22, 2017*

**Algebra I**

I would do it this way: Amount of pure water needed --- x gal Amount of the 60% stuff ------ 6-x .6(6-x) + 0x= .5(6) 3.6 - .6x = 3 -.6x = -.6 x = 1 so use 5 gal of the 60% plus 1 gal of pure water your answer of 7.5 gal should have made no sense to you. You want to end up with...

*February 22, 2017*

**Algebra**

Don't use x as a multiplication sign, use * or use brackets, so I see your product as (a)(b)(a)(b) = (ab)^2 or = a^2 b^2 when you say ab^2, it is only the b that is squared.

*February 22, 2017*

**Derivative-Optimization Problems**

side parallel to river --- y m each of other two sides --- x 2x + y = 600 ---> y = 600-2x area = xy = x(600-2x) = -2x^2 + 600x d(area)/dx = -4x + 600 = 0 for a max of area -4x = -600 x = 150 then y = 600-2x = 300 largest area = 150(300) = 45000 m^2

*February 22, 2017*

**Math**

your equation: y = 80 + 10n your brother's equation: y = 275 - 15n b) when does 80+10n = 275-15n ? c) whatever you got for n in b) sub this into "your" equation

*February 22, 2017*

**Algebra**

.125 , .125r, .125r^2, .125r^3, .125r^4, .125r^5, 8 .125r/.125 = 8/.125r^5 r = 64/r^5 r^6 = 64 r = ± 2 set 1: .25, .5, 1, 2, 4 set 2: if r = -2 -.25, .5, -1, 2, -4

*February 22, 2017*

**maths**

make a sketch. draw poles AB and PQ with B and Q on the ground Draw the reflection of AB in the horizontal and call it BA'. Joint A' to P Label the intersection of A'P with BQ as M. let BM = x, then MQ = 20-x Of course the shortest distance between any two points ...

*February 22, 2017*

**Math word problem**

here is your problem: 1.50(x) + 4.00(y) = 712 1.50(x) + (y) = 712/4 you divided the 2 last terms by 4, but not the first one

*February 22, 2017*

**Maths**

Use the formula for the sum of terms (7/2)(2a + 6d) = (13/2)(2a + 12d) times 2, then expand 14a + 42d = 26a + 156d -12a = 114d a = -19/2 d sum(20) = 10(2a + 19d) = 20a + 190d = 20(-19/2 d) + 190d = 0

*February 22, 2017*

**Algebra**

I read your (f of g)(x) as f( g(x) ) By the "Just look at it" theorem, if g(x) = x+3 and f(x) = 1/x^3 then f(g(x)) = f(x+3) = 1/(x+3)^3 , which is h(x)

*February 22, 2017*

**math**

We don't do assignments for students. What part of this do you find difficult? Most are formula-based questions which you must have in your notes.

*February 22, 2017*

**Math**

(4z^2 + 7z – 8)(–z + 3) = -4z^3 + 12z^2 - 7z^2 + 21z + 8z - 24 = -4z^3 + 5z^2 + 29z - 24 matching this with –4z3 + xz2 + yz – 24 5z^2 = xz^2 ----> x = 5 29z = yz -----> y = 29

*February 22, 2017*

**ss**

strongly linked, they are each other's largest trading partner.

*February 22, 2017*

**maths**

Is this translation correct ? A rectangular field is 15 m long and 9 m wide. It has a path 1.5 m wide all around it. Find the area of the path. area of field = 15(9) m^2 =.... area of the whole thing = 18(12) m^2 = ..... (make a sketch to see where the 18 and 12 come from) ...

*February 22, 2017*

**Math**

Ruby now ---- x Pawan now --- 2x 3 years ago: Ruby --- x-3 Pawan -- 2x-3 2x-3 = 3(x-3) carry on

*February 22, 2017*

**Algebra**

Rider: y = .5x + 50 UMove: y = .75x + 45 Just follow the instructions, they are quite clear.

*February 22, 2017*

**Math**

solve: x^3 + 3x + 1 = -3 x^3 + 3x + 4 = 0 let x = 1 ---> 1+3+4 = 0 ? no let x = -1 ---> -1-3+4 = 0 , yeahh x^3 + 3x + 4 = (x+1)(x^2 - x + 4) = 0 so x=-1 or x is a complex number so f^-1 (-3) = -1 check: f(x) = y = x^3 + 3x + 1 f(-1) = -1 -3 + 1 = -3 the inverse is: x = y...

*February 22, 2017*

**Math**

and a rhombus

*February 21, 2017*

**pre-algebra**

1. It said: "The length of a yard is triple the length of the garden" --> so if you let the length of the garden be x then the length of the yard is 3x (we could have used any variable name, you used G, that's fine) It said: "the difference between the ...

*February 21, 2017*

**Calculus (RATE OF CHANGE)**

Make a sketch and use the cosine law: let the rate of the slower car be x mph then the rate of faster car is 2x mph Let the distance covered by the slower car by x then the distance covered by the faster car is 2x let the distance between them be d d^2 = x^2 + 4x^2 -2x(2x)...

*February 21, 2017*

**Calculus (RATE OF CHANGE)**

I assume you want dy/dx y = 1/x + 2 dy/dx = -1/x^2 when x = 2 dy/dx = -1/4

*February 21, 2017*

**Math**

I think you have a typo. You want a 6th added, so there should have been 5 of them given already. You only have four of them

*February 21, 2017*

**Calculus**

see my previous reply, in this case multiply each term by 7, then go from there

*February 21, 2017*

**Calculus**

Some authors consider 18x + y = 13 to be "standard" form , and 18x + y - 13 = 0 to be "general" form Look at your text or notes

*February 21, 2017*

**calculus**

Are there supposed to be exponents in your equation?? I will assume: V = ?aT^3 + bT^2 ? cT + 1 , using the given: dV/dT = -3a T^2 + 2b T - c I assume you plugged in the given values for a, b, and c, used the quadratic equation formula and solved for T Since the coefficient of ...

*February 21, 2017*

**pre-algebra**

number of votes for Michael --- M number of votes for Tina = M - 200 number of votes for Sam = M + 4200 (you had that, good!) Now, just translate: "Samantha plus the number of votes received by Michael minus the number of votes received by Tina (M + 4200) + M - (M-200) = ...

*February 21, 2017*

**Algebra**

You should define your variables, hard to check without knowing what x stands for e.g. let the "other " angle be x then "one" angle is 4x+2 "The third angle is three times the first angle decreased by 6" ---> poor wording. How do we know which ...

*February 21, 2017*

**Math**

certainly not linear, slopes between pairs of points would have to be the same, --- they are not. Took differences in the y values up to the fourth difference columns. No constant so , no polynomial up to 4th degree. Not even Wolfram found an equation, when to least-fit ...

*February 21, 2017*

**Math, data management**

no, you probably meant 10!/(4!,3!,3!) = 4200

*February 21, 2017*

**Algebra**

see http://www.jiskha.com/display.cgi?id=1487716112 this is very similar, except you would have 1/x and 1/2x as the combined rate, and you know that result.

*February 21, 2017*

**Algebra**

look at the solution both Damon and I gave here for a similar question http://www.jiskha.com/display.cgi?id=1487716112 The only difference is that here you are given the combined rate.

*February 21, 2017*

**Math - Calculus**

Make a sketch. Your rock will travel in a circle whose equation is x^2 + y^2= 9 you must release it at a point P(x,y) so that it reaches a point (15,0) Anyway, we have right-angled triangle , (at the point of release, the angle is 90° between radius and tangent. let the ...

*February 21, 2017*

**Algebra**

rate of old machine = 1/170 rate of new machine = 1/119 combined rate = 1/170 + 1/119 time at combined rate = 1/(1/170+1/119) = 1/(1/70) = 70 minutes

*February 21, 2017*

**Algebra**

one number --- x the other ------ x-32 1/(x-32) + 5(1/x) = 1/6 times 6x(x-32) 6x + 30(x-32) = x(x-32) 6x + 30x - 960 = x^2 - 32x x^2 - 68x + 960 = 0 (x-20)(x-48) = 0 x = 20 or x = 48 if x = 20 then the other is negative, but both our numbers are to be positive so x = 48 and ...

*February 21, 2017*

**Math**

v = -32t + 28 Is there a question?

*February 21, 2017*

***** Monitor Needed For Banning**

Mehdi Moustaoui

*February 21, 2017*

**algebra**

x(500) = .1(200) + .2(300) x = 80/500= .16 change my answer to a percent.

*February 21, 2017*

**Math**

we can find the equation of the line, you have the slope and a given point. Once you have the equation, replace the x with anything you want, then find its matching y value

*February 21, 2017*

**Algebra**

3.18x+2.6+0.9x+x=28 5.08x = 24.4 x = 24.4/5.08 = 5 Hali's equation of 5.1x = 25.4 -->(no idea where that came from ) does not yield the solution of x = 5 as he concluded.

*February 21, 2017*

**Math**

This looks like an assignment or test. I don't see your choices for the answers nor any indication where you had difficulty. You weren't expecting somebody to just do this for you, did you ?

*February 21, 2017*

**kishore**

originial fraction ---- a/b case 1: (a+1)/(b+3) = 1/2 2a +2 = b+3 ----> 2a - b = 1 or b = 2a-1 case 2: (a-1)/(b+2) = 2/5 5a - 5 = 2b+4 5a - 2b = 9 use substitution: 5a - 2(2a-1) = 9 a = 7 , then b = 13 the original fraction was 7/13

*February 21, 2017*

**math**

your height equation must be h = -4.5t^2 + 25t + 50 so you want to solve: 7 = -4.5t^2 + 25t + 50 4.5t^2 - 25t - 43 = 0 use the quadratic formula, discard any negative value of t

*February 21, 2017*

**Mathematics**

What is 1 - (.9)^5 ?

*February 21, 2017*

**math**

right now: 40 people signed up, $120 per person. let the number of additional skiers be m number going : 40+m cost per skier : 120-2m revenue = (40+m)(120-2m) = 4800 + 40m - 2m^2 This is a quadratic, a parabola opens down, so it has a maximum revenue. This is found by finding ...

*February 21, 2017*

**Maths**

I will assume compound interest, i = .06/12 = .005 amount = 12000(1.005)^42 = .... subtract the original 12,000 to find the interest. for interest earned after 2 years = 12000(1.005)^24 - 12000 "How much interest is earned each year " - this would require 42 ...

*February 21, 2017*

**Math**

I made a sketch on a grid, I labeled the point at the anchor (0,2) and the point of atachment at the pole as (x,45) (45-2)/(x-0) = 3/5 3x = 215 x = 215/3 Now , use the formula for the distance between 2 points

*February 20, 2017*

**Algebra**

Your equation should have been 25y^2 - 60y + 324 = 0 by the formula: y = (60 ±?-28800)/50 = (60 ± 120?-2)/50 = (6 ± 12i?2)/5 which is a complex number

*February 20, 2017*

**maths**

speed at remaining distance ---- x km/h (2/3)(450)/75 + (1/3)(450)/x = 13/2 300/75 + 150/x = 13/2 times 2x 8x + 300 = 13x carry on

*February 19, 2017*

**math**

I agree with Bosnian's answer. check your typing of the question. Did you perhaps mean ?15/(9y) < 11/13 ?

*February 19, 2017*

**Math**

At the moment she steps off, her linear velocity equals the rate the arc length is increasing. circumference = 2?(25) = 50? ft 36° = 36/360 = 1/10 of a rotation so the linear velocity of any point is 5? ft/second 5? ft/1 second = (5?/5280) / (1/3600) miles/hour = (5?/(5280...

*February 19, 2017*

**Algebra**

So I assume it is 4x^3 = 16 then: 4x^3 - 16x = 0 4x(x^2 - 4) = 0 4x(x+2)(x-2) = 0 x - 0, ± 2

*February 18, 2017*

**MATH (POST 2) Need Help Please**

I am not familiar with the "average daily balance method " , I don't live in the US. Perhaps one of the other math tutors can help out here.

*February 18, 2017*

**Algebra**

Apparently we are supposed to ignore the loss due to saw-cuts, a bad idea. Looks like we have two verticals and 3 horizontal pieces. let each of the verticals be x and each of the horizontals be y 2x + 3y = 72 inches y = (72-2x)/3 volume = 24(x)(y) = 24x(72-2x)/3 = 576x - 16x^...

*February 18, 2017*

**Algebra**

length ---- x width ----- y 2x+2y = 42 x+y = 21 y = 21 - x printing area: length = x-2 width = y-3 = 21-x - 3 = 18-x area = (x-2)(18-x) = 18x - x^2 - 36 + 2x = -x^2 + 20x - 36 since this is a downwards parabola, the vertex will be the answer to your question. Find the vertex ...

*February 18, 2017*

**Math**

"Guessing" ??? Good grief, this is math. $8 to rent a car for 15 days ????? just plug in your data .... C = 50(15) + .15(475) = ......... I am sure you have a calculator if you can't do it with pencil and paper.

*February 18, 2017*

**math**

(x/50)+(x/25)+(3x/50)+(2x/25)+...+2x = x/50 + 2x/50 + 3x/50 + 4x/50 + ... 100x/50 = (x/50)( 1+2+3+4+ ... + 100) continue

*February 18, 2017*

**math**

slower speed ---- x km/h faster speed ----- x+6 km/h 5x + 4(x+6) = 294 easy to solve....

*February 18, 2017*

**math**

(4xy+2xy)^2 did you notice that you have like terms, so = (6xy)^2 = 36 x^2 y^2

*February 18, 2017*

**math**

P(A or B) = P(A) + P(B) - P(A and B) your data fits that formula

*February 18, 2017*

**@ penny - math**

Penny, it is you who determines if you fail or pass, please don't blame Steve.

*February 18, 2017*

**Math**

Use your formulas ar = -6 ar^4 = 48 divide them: r^3 = -8 r = -2 now find a, then use the formula for the sum(n) terms let me know what you get, so I can check it

*February 18, 2017*

**math**

How many 5's do you see on 1 die ??

*February 18, 2017*

**Algerba**

Well, why don't we solve it, probably faster than subbing in all those values -1.5^2+4x+2.2=0 3x^2 - 8x - 4.4 = 0 x = (8 ± ?116.8)/6 = appr 3.13 or -.5 you are right

*February 18, 2017*

**maths**

list the first prime numbers, add them up, then divide by 10 remember the first prime number is 2, then 3, etc

*February 18, 2017*

**Algebra I**

4p - 2m = 2 ---> 2p - m = 1 or m = 2p-1 3p + 9m = 54 sub in m=2p-1 into the other equation and solve

*February 18, 2017*

**math**

how many kings ? how many hearts ? remember not to count the king of hearts twice, it would be included in both counts.

*February 18, 2017*

**maths**

so you have 2/5 left (2/5)x = 80 2x = 400 x = 200 check: take 3/5 of 200 and subtract it from 200. What do you have left ?

*February 18, 2017*

**@ Steve - MATH**

Nice!!! Well, I always like to take those long detours. I once went from Toronto to Niagara Falls by going all the way around Lake Ontario.

*February 18, 2017*

**MATH**

cos 4A = cos^2 2A - sin^2 2A = (cos 2A - sin 2A)(cos 2A + sin 2A) = (cos^2 A - sin^2 A - 2sinAcosA)(cos^2 A - sin^2 A + 2sinAcosA) from cosA = 1/2 ----> sinA = ?3/2 (A = 60° or ?/3) plug the cos and sin values into my last equation and evaluate, I will leave the ...

*February 18, 2017*

**math**

(1/3)p = 2 p = 6

*February 18, 2017*

**Geography**

The angle between is 150° which is 150/360 or 5/12 of a rotation. 5/12 of 24 hours is 10 hours. so the time would be 5:30 - 5:00 = 19:30 ---> evening of previous day ( that would be 7:30 pm using US notation) time decreases from east to west

*February 18, 2017*

**algebra 2**

my starting equation would be: y-5 = -1(x+3) re-arrange it to see which one fits

*February 17, 2017*

**Algebra 1**

What makes you "think" it is either a or c What did you do to get the answer?

*February 17, 2017*

**algebra**

What are you doing ???? (4275)(4372) = 18,690,300

*February 17, 2017*

**math**

your number ---- x x/4 + 5 - 6 = 6 x/4 = 7 multiply both sides by 7 x = 28 try it.

*February 17, 2017*

**math**

I think that should be 48 done 6 years ago by MathMate http://www.jiskha.com/display.cgi?id=1307634385

*February 17, 2017*

**math**

you have posted 4 disconnected statements 215 = 0.73n ----> false n = 0.73 × 215 ----> does not follow from the previous, but would be correct 0.73 = n × 215 -----> does not follow from the previous 215 = 73n ---> does not follow the previous, but ...

*February 17, 2017*

**Math**

suppose we use an example: e.g. f(x) = (x-5)^2 + 3 , which is a parabola with vertex (5,3), opening upwards f(2-x) = (2-x - 5)^2 + 3 f(2-x) = (-x - 3)^2 + 3 f(2-x) = (x+3)^2 + 3 , (just like (-9)^2 = 9^2 ) -f(2-x) = -(x+3)^2 - 3 so we have a reflection in the x-axis, and a ...

*February 17, 2017*

**Math**

let the length be x let the breadth be y perimeter = 2x + 2y given : length : perimeter = x : 2x+2y = 1:3 x/(2x+2y) = 1/3 3x = 2x+2y x = 2y length : breadth = x : y = 2y:y = 2 : 1

*February 17, 2017*

**Maths**

The way you typed it, ?h^2 would simply be h Is that what you want or did you mean: A=?r?(h²-r²) -----> critical brackets I will wait for your reply

*February 17, 2017*

**math**

Just noticed that Steve answered the same question 3 years ago, when it was stated as a complete question http://www.jiskha.com/display.cgi?id=1392441787

*February 17, 2017*

**math**

So ?

*February 17, 2017*

**math**

place 1 on its place on a number line, now count 15 to the right, then 15 to the left I get 16 with1 and -14 with 1 how far from 1 to 16 ? how far from -14 to 1 ?

*February 17, 2017*

**Mathematics**

Assuming that "bearing" to you means North = 0 and you are going clockwise. Make a sketch and complete the right-angled triangle: sin20° = y/50 ---> y = 50sin20 = appr 17.1 km or cos70° = y/50 ---> y = 50cos70 = appr 17.1 km

*February 17, 2017*

**Maths**

Let's compare the value of $1 at the end of 10 years at both types of interest: compound: Value = 1(1.06)^10 simple: let the rate be r interest = 1(10)(r) = 10r value = 1 + 10r so 1 + 10r = 1.06^10 10r = 1.790847... - 1 r = .0790847... rate = 7.91% to 2 decimals

*February 17, 2017*

**Math**

the general term of an AS is a + (n-1)d, where a is the first term, d is the common difference, and n is the number of terms so : a = 0 a+9d = 15 0+9d = 15 d = 15/9 = 5/3 For 10 to be one of the terms a + (n-1)d = 10 0 + (n-1)(5/3) = 10 times 3: 5(n-1) = 30 5n-5 = 30 5n = 35 n...

*February 17, 2017*

**Algebra**

(x-1/2)-(x-2/2)+(x-3/2)-...-(x-100/2) = x - 1/2 - x + 2/2 + x - 3/2 - .... - x + 100/2 = x-x+x-x+x-....-x -1/2 + 2/2 - 3/2 - ... + 100/2 looking at the last term, we see there are 100 terms, so the x's drop out = -1/2 + 2/2 - 3/2 - ... + 100/2 = (-1/2)(1 - 2 + 3 - .... + ...

*February 17, 2017*

**3rd Math fraction answer conflict**

You are correct at 36/7 another way to look at it: there are 12 half-hours in 6 hours. Have Katie look at a clock. So the length is 12*(6/7) = 36/7 inches

*February 16, 2017*

**Math**

In your trig repertoire , you should know the 3 basic trig values of angles 0°, 30°, 45°, 60°, 90° by knowing the ratio of sides of the 30-60-90 and the 45-45-90 degree triangles. This is very very important in any further study of trig. I will do the only...

*February 16, 2017*

**Math**

FG----> 25+6.5n, where n is the number of games GB ---> 57 + 2.5n 25 + 6.5n = 57 + 2.5n 6.5n - 2.5n = 57 - 25 carry on

*February 16, 2017*

**Math**

hint: sure looks like the coach is collecting $22 from each player. So on Friday, he collects from 2 players, or $ .....? So from p players, he collects $ .... ?

*February 16, 2017*