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March 23, 2017

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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

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