Saturday
December 20, 2014

Posts by Reiny


Total # Posts: 28,259

Math
at a time of t min, let the height of the water level be h m, and the radius of the water level be r m By ratios: r/h = 4.5/9 = 1/2 2r = h or r = h/2 Volume of cone = (1/3)π r^2 h = (1/3)π (h/2)^2 h = (1/12)π h^3 dV/dt = (1/4)π h^2 dh/dt given: when h = 4 m...
October 5, 2014

Algebra
by definition: p-10 = 20 OR -p+10 = 20 p = 30 or -p = 10 p = 30 or p = -10
October 4, 2014

Math
-80=8b-15+5b -80 + 15 = 13b or 13b = -65 b = -5 Solving an equation means finding that value of the variable which makes the original equation a true statement. We found that value to be b = 5 Now sub that value into the left side and the right side of the ORIGINAL equation. ...
October 4, 2014

Math Help
should have noted that the original function is only valid for x ≤ 1
October 4, 2014

Math Help
I will assume you meant f(x) = -5√(-4x+4) + 2 or else they would have just added the 2 to the 4 y = -5√(-4x+4) + 2 = -10√(1-x) + 2 , I factored out √4 which is 2 inverse: interchange x and y variables x = -10√1-y) + 2 solve this new equation for y...
October 4, 2014

Pre-Calc
number of apples processed = P(22) = .... do the arithmetic cost = C(P(22)) = put the answer of P(22) into C(n)
October 4, 2014

Math
I assume you meant √(21x) , and not the way you typed since 21 = 3x7 , you want either another 3 or 7 in x so that we have at least one perfect square. none of the first 3 choices contain a 3 or 7 ,but 54 does so √(21x54) = √3x7x3x9x2) = √(81*14) = 9&#...
October 4, 2014

Math
sum of all exterior angles of an n-gon is 360 so 360/n = appr 30 n = 12 It is a 12-gon
October 3, 2014

Math
sum of angles of a regular polygon = 180(n-2) so 180(n-2)/n = 165 180n - 360 = 165n 15n = 360 n = 24 sum of inside angles = 180(22) = 3960°
October 3, 2014

Math
sum of interior angles of a heptagon = 5(180) = 900 so we have 520 + x + x + (3/2)x = 900 2x + 1.5x = 380 x = appr 108.57° take it from here
October 3, 2014

(MCV4U) Vectors
ignore the first part of my solution, start with My diagram ...
October 3, 2014

(MCV4U) Vectors
Since you labeled your subject as vectors I will use them let the wind vector be (rcosØ, rsinØ (rcosØ, rsinØ) + (200cos180,200sin180) = (180cos170,180sin170) ( rcosØ, rsinØ) = (22.7346 , 31.2567) 2r^2 = 22.7346^2 + 31.2567^2 r = 27....
October 3, 2014

Algebra
6x/16 + 1/16 = (6x+1)/16
October 3, 2014

Math
Are you sure the sum of the other two regions is 25a and not 24a ? then the sum of the area would be a^2 + 144 + 24a = (a+12)^2 which would make it a square of sides a+12 for a perimeter of 4a + 48
October 3, 2014

math
2 chicken lay 8 eggs in 3 days 1 chicken lays 4 eggs in 3 days 1 chicken lays 8 eggs in 6 days 5 chicken lay 40 eggs in 6 days
October 3, 2014

5th grade math
16/5 - 2 = 6/5 (6/5)/2 = 3/5 or 60%
October 3, 2014

math
(x+2y)^2 = (x+2y)(x+2y) = x^2 + 2xy + 2xy + 4y^2 = x^2 + 4xy + 4y^2 The method I used is sometimes referred to a FOIL
October 3, 2014

Pre-Calc/Trig...
You are correct
October 3, 2014

Analytic Geometry CHECK MY ANSWER
the slope is (6-3)/(2-2) = 3/0 which would be undefined. None of the choices are correct Your line is a vertical line.
October 3, 2014

Analytic Geometry CHECK MY ANSWER
your equation should read: t = 85n + 25 Doesn't the value of t "depend" on what you put in for n ?? So t would be the "dependent" variable, so that implies that ....... your choice of answer makes no sense. You mean to say that the total t is not ...
October 3, 2014

Pre-Calc/Trig...
yes and yes
October 3, 2014

Pre-Calc/Trig...
how about letting t = 1, 2, 3, 4, ... minutes and then interpret the results. What do you notice about the distance for every minute of change in time.
October 3, 2014

Pre Calc
so you want: 7000(1.07^t) = 1400 1.07^t = 2 take log of both sides, and by the rules of logs t log 1.07 = log 2 t = log2/log1.07 = appr 10.245 years
October 3, 2014

Pre-Calc/Trig...
so in f(x) = 1/(x+2) you are replacing x with 3+h so f(3+h) = 1/(3+h + 2) = 1/(h+5)
October 3, 2014

Algebra 1 Check
correct do you know why ?
October 3, 2014

Math Questions
I will do the first one: 6√24x = 18√24 divide by √24 6x = 18 x = 3 do the others the same way, #1 and #3 are incorrect, you had #2 correct btw, I interpreted you question as you typed it. I assume you did not mean 6√(24x)
October 3, 2014

Math
for y = cos kt the period would be 2π/k since the period of sec is the same as the period of sin period = 2π/(π/5) = 2π(5/π) = 10 Didn't it tell you that at the beginning ?
October 3, 2014

math
You must have been given some choices in the range to give you .34
October 3, 2014

Math
V = πr^2 h, but h = 2r so V = πr^2 (2r) = 2πr^3 then 2πr^3 = 250 r^3 = 125/π r = cuberoot(125/π) h = 2r = 2 cuberoot(125/π) = appr 6.83 cm
October 3, 2014

Math
correct
October 3, 2014

math
depends what results you want. Incomplete question .
October 2, 2014

Math Question
so y = k/x sub in the values 63 = k/3 k = 189 so .......
October 2, 2014

Algebra
since each bracket has a +1 understood in front of it, you can just drop the brackets. Collect all like terms and you are done
October 2, 2014

Math 3 quick questions
For the first two, do you notice that the binomial appears both as a square and as a first degree expression? When you first learn to do these types, it might be a good idea to replace the binomial with a single variable. e.g. in the first: let 3x+1 = a , then your equation ...
October 2, 2014

algrebra
number of dimes --- x number of quarters --- x+17 value of money: 10x + 25(x+17) = 600 , all in cents 10x + 25x + 425 = 600 35x = 175 x = 5 so 5 dimes and 22 quarters. check by finding the value of 5 dimes and 22 quarters.
October 2, 2014

Math
14 g = 53 L 1 g = (53/14) L then 25 g = (53/14)(25) L = appr 94.6 L
October 2, 2014

Math
what happens when you multiply something by 10? what happens when you multiply something by 100? by 1000? etc so look at 60x50 as 6x10 x 5x10 = 6x5x10x10 = 30x100 = 3000
October 2, 2014

geometry
You are obviously looking at some diagram, which we can't see.
October 2, 2014

math
It is unfortunate that measurement of angles, and time, has escaped the metric system. Things would be so much easier. K = 90° - 48° 26' 8" = 89° 59' 60" - 48°26'8" = 41° 33' 52" Hint: If you have a good scientific ...
October 2, 2014

HELP! Algebra. DONT UNDERSTAND
Niezel is correct from a - e explanation of e) (a+b)(c+1)-(a+b) = ac+bc = c(a+b) by common factor of (a_+b) = (a+b)(c+1 - 1) = c(a+b) f) x^2 - 9y^2 ----- standard difference of squares = (x+3y)(x-3y) g) (x^2 - y^2) + x + y = (x-y)(x+y) + (x+y) , difference of squares at the ...
October 2, 2014

Financial Mathematics
i = .07/12 = .0058333... (I stored that in memory on my calculator for good accuracy) 2000(( 1.0058333..^20 - 1)/.0058333)(1.0058333..)^40 + 2500( (1.00583333..^20 - 1)/.0058333..)(1.0058333..)^20 + X(1.005833..^20 - 1)/.0058333.. = 180000 , X = 2000+R 53375.555 + 59392.5459...
October 2, 2014

Probability
a) prob(red) = 5/10 = 1/2 b) prob(red or white) = 7/10 c) prob( as stated) = 5/10 or 1/2 , there are still 10 balls, since you replaced it whatever happened in first draw has no effect on the second draw d) prob( as stated) = 5/9 , now it matters, there are only 9 balls left e...
October 2, 2014

math
First of all the area of a circle is π r^2 , not (πr)^2 so πr2= 658 r^2 = 658/π r = √(658/π) = appr 14.47
October 1, 2014

Math
prob(fail) = 6/100 = 3/50 prob(not fail) = 47/50 prob(2 of 6 will fail) = C(6,2) (3/50)^2 (47/50)^4 = appr .042 Since the prob (anything) must be a number from 0 to 1, your answer makes absolutely no sense at all. I don't even understand your notation.
October 1, 2014

Math
y - y1 = mx - mx1 mx1 = mx - y + y1 x1 = (m - y + y1)/m
October 1, 2014

Trigonometry
safe ramp: tanØ = 1/12 Ø = 4.76° Since your angle is greater than that, it is not safe
October 1, 2014

Math
4√(1280r^4t^12) = 4√1280 √r^4 √t^12 = 4(16√5)r^2 t^6 = 64√5 r^2 t^6
October 1, 2014

Math Definition Help
Definitions are easy to check Let Google or your texbook be you friend.
October 1, 2014

Math Help
I will assume you meant f(x) = (3x+4)/5 or y = (3x+4)/5 step1: interchange the x and y variables x = (3y+4)/5 step2: solve this inverse equation for y 5x = 3y + 4 3y = 5x - 4 y = (5x-4)/3 f^-1 (x) = (5x-4)/3
October 1, 2014

Pre-Calc
A and B are inverses. (you can check by picking any number, subbing that into the original function. Take that answer and sub it into the "inverse" function. If you don't get back the original number it is not a true inverse. e.g. for D let x = 3 f(3) = 7 f(7) = ...
October 1, 2014

MATH
I will assume you meant: ln ( (3x-2)/(x-1) ) < 0 I would establish the boundary by letting ln ( (3x-2)/(x-1) ) = 0 then (3x-2)/(x-1) = e^0 , yes e^0 = 1 (3x-2)/(x-1) = 1 3x-2 = x-1 2x = 1 x = 1/2 So we need either x < 1/2 or x > 1/2 But remember x = 1 is not allowed ...
October 1, 2014

Math
1. Use the sum of n terms of an arithmetic sequence sum = (n/2)(first + last) (16/2)(first + 12500) = 800000 divide by 8 first + 12500 = 80000 first = 80000-12500 = 67500 2. museum A: a = 50,000 , d = 2500 museum B: a = 45,000 , d = 2750 find term(12) or a+11d for each one ...
October 1, 2014

Maths
Your formula makes no sense, because I could just cancel the d's and get l = k check your typing. Is there a square root somewhere I suspect something like: " intensity is proportional to the square of the distance"
October 1, 2014

Pre Calculus
I did the same question on Monday http://www.jiskha.com/display.cgi?id=1412031500
October 1, 2014

MATH
Lena,did you not check your answer? It does not work, mine does. Always check your results by testing them for the original conditions 14(.25) + 22(.50) ≠ $15.00
September 30, 2014

MATH
You should check your "caps lock" key, it appears to be stuck. number of 1/2 cups ---- x number of whole cups --- 37-x 25x + 50(37-x) = 1500 25x + 1850 - 50x = 1500 -25x = -350 x = 14 etc
September 30, 2014

7th grade math
Correct, there are 10 of them and you found them all
September 30, 2014

Math
Here is how I would do this in a formal way: Would like to have a zero on the right side, so ((3x-2)/(x-1))<1 ((3x-2)/(x-1))-1 < 0 (3x-2 - (x-1))/(x-1) < 0 (2x - 1)/(x-1) < 0 "critical values" are x = 1/2 and x = 1 This splits a number line into 3 parts, ...
September 30, 2014

math
helicopters --- H airplanes ----- 4H H+4H = 35 5H = 35 H = 7 so .....
September 30, 2014

Math .
#1 yes #2: a+5 = (1/5)(5a+25) a+5 = a+5 ----> 5=5 , statement is true infinite number of solutions #3 3(4x - 3) - 7x = 5x - 9 12x-9-7x=5x-9 5x-9 = 5x-9 true, so infinite number of solutions #4 yes
September 30, 2014

Calculus
the original fractions had 7 and 5 in the denominator which is the same as (1/7) times .... e.g 9/4 = (1/4)(9)
September 30, 2014

Calculus
recall that if y = secx dy/dx = secx tanx y= [(sec^7 x)/7] - [(sec^5 x)/5] dy/dx = (1/7)(7)(sec^6 x)(secx)tanx - (1/5)(5)(sec^4 x)secx tanx = sec^7 x tanx - sec^5 x tanx = sec^5 x tanx(sec^2 x - 1) but sec^2 x - 1 = tan^2x = (sec^5 x)(tan^3 x) nice question
September 30, 2014

Pre-caluclus
so ln(x-2e)+ln(x-3e)=2 ln ( (x-2e)(x-3e) ) = 2 by definition (x-2e)(x-3e) = e^2 x^2 - 5ex + 6e^2 - e^2 = 0 x^2 - 5ex + 5e^2 = 0 x = (5e ± √(25e^2 - 4(1)(5e^2))/2 = (5e ± √5e^2)/2 = (5e ± e√5)/2 = ( (5±√5)/2 )e
September 30, 2014

analytic geometry
horizontal distance --- x I see it as: tan 3.5° = 120/x x = 120/tan3.5 = appr 1962 ft
September 30, 2014

Math
only one possibility of rolling a number less than 2, namely the number 1 prob(one) = 1/6 number of times this happens rolling 720 times = (1/6)(720) = 120
September 30, 2014

Algebra
|x+2| < 5 x+2 < 5 AND -x-2 < 5 x < 3 AND x > -7 I always taught this notation: -7 < x < 3 I will let you convert to your notation
September 30, 2014

math
let's change the room dimensions to inches 14 ft by 20 ft = 168 in by 240 in We can fit 21 tiles along the 168 inches side We can fit 30 tiles along the 240 inches side number of tiles = 21 x 30 or 630 tiles. The solution by Brilliant was not so brilliant, it is wrong ...
September 30, 2014

THEORY OF INTEREST
let the equivalent nominal rate compounded quarterly be j Consider one year. (1+.087/12)^12 = (1 + j/4)^4 1.00725^3 = 1+j/4 .051908068 = j/4 j = .087632274 or 8.763 %
September 30, 2014

Algebra 2 Answer Check
nope,, Damon showed you that the slope of your given line is -5/2 Trust him !
September 30, 2014

Math
1. the inverse of your given relation is (-1,3) , (5,2) , (-4,-4) 2. can you see what I did? I suggest you plot the original points and join them with a line, then plot the new points and join them with a line. Can you see what happened ?
September 30, 2014

Pre-Calculus/Trigonometry
how about we let f(x) = x^2 g(x) = x/(x+4) then g(f(x)) g(x^2) = x^2/(x^2 + 4)
September 30, 2014

precal
or , using the standard a to be first term, r the common ratio ar^12 = -72 ar^9 =9 divide them r^3 = -8 r = -2 , then from ar^9 = 9 a = 9/(-2)^9 = -9/512 term(7) = ar^6 = (-9/512)(-2^6) = -576/512 = -9/8
September 30, 2014

Math Gr.12
Finding the vertex would give you the answer what method have you learned to find the vertex?
September 30, 2014

Pre-Cal
According to the directions Average cost = (300+5x)/x
September 30, 2014

College Prep Math 4
2√(5x) = 100 √(5x) = 50 square both sides 5x = 2500 x = 500
September 30, 2014

Math Gr 12
h = -4.9t^2 + 29.4t for the initial height, t = 0 , so h = 0 "reach the ground" implies h = 0 -4.9t^2 + 29.4t = 0 t(-4.9t + 29.4) = 0 so t = 0 ----> the initial time and height or t = 29.4/4.9 = 6 so it will return to the ground after 6 seconds
September 30, 2014

math- pre calc/trig
Bosnian is simply using the Pythagorean Theorem , where he called each of the sides a and the diagonal d d^2 = a^2 + a^2 2a^2 = d^2 2a^2 = (7√2)^2 = 98 a^2 = 49 a = 7
September 30, 2014

college algebra
nice parabola, what about it ?
September 29, 2014

Math
1. did you mean 4/(3 + √5) or 4/3 + √5 , the way you wrote it. secondly, what do you want to "solve" ? are you studying rationalizing the denominator? My question also applies to the other two questions
September 29, 2014

Math
clearly 4y(y^2+1)(2y^2+1) Always check your factored answer by expanding it again to make sure the original comes back
September 29, 2014

Math
looks like a common factor of 4y can you finish it?
September 29, 2014

Precalculus
First of all , let me point out a discrepancy in the wording of your question The way your equation is written as y = x^2 + 9x - 36 it should have asked for the x-intercepts of the function To do that , we realize that for an x-intercept, the value of y = 0 so your function ...
September 29, 2014

Math
your number is 2*3*5*7 = 210 Now for factors take any combination of single factors --- 4 of them pairs of factors -- you should find 6 of them triples of factors --- you should find 4 of them all of them ---- clearly the number 210 itself
September 29, 2014

algebra
write it this way: (1+x)/(1+x^2) = 2/5 cross-multiply 2 + 2x^2 = 5 + 5x 2x^2 - 5x - 3 = 0 (x - 3)(2x + 1) = 0 x = 3 or x = -1/2
September 29, 2014

Math
done when you posted under a different name, why did you switch names ? http://www.jiskha.com/display.cgi?id=1412031500
September 29, 2014

Calculus
e^-x √(3e^(2x) - 5/4) = e^x multiply both sides by e^x √(3e^(2x) - 5/4) = e^2x square both sides 3e^(2x) - 5/4 = e^4x times 4 12 e^2x - 5 = 4e^4x 4e^4x - 12 e^2x + 5 = 0 (2e^2x - 1)(2e^2x - 5) = 0 e^2x = 1/2 OR e^2x = 5/2 if e^2x = 1/2 ln both sides 2x lne = ln1 - ...
September 29, 2014

Math
Each "pair" of factors allows a rectangular arrangement so which number has more factor pairs, 75 or 60 ? e.g. factor pairs of 75 1 75 3 25 5 15 and 60 ?
September 29, 2014

math
let's intersect them: -x^2 - 3x + 6 = 3x + k -x^2 - 6x + 6-k = 0 x^2 + 6x + k-6 = 0 to have 2 distinct real solutions , the discriminant must be > 0 b^2 - 4ac > 0 36 - 4(1)(k-6) > 0 36 -4k + 24 > 0 > 0 -4k > -60 k < 15 Notice in my graph, when k = 0, ...
September 29, 2014

Algebra
cost = 65 + 75t so if 65+75t = 196.25 75t = 131.25 t = 1.75 so the job took 1 hour and 45 minutes, I will let you figure out when the job was done
September 29, 2014

AP Calc B/C
Wolfram says: http://integrals.wolfram.com/index.jsp?expr=e%5Ex%2F%281+-+e%5E%282x%29%29%5E%283%2F2%29&random=false
September 29, 2014

Algebra
Go with PsyDAG's solution, I hit the 3 key instead of the 2
September 29, 2014

Algebra
number of marbles in each bag --- x 3x + 3 = 29 3x=27 x=9 each bag has 9 marbles
September 29, 2014

Pre-Calculus/Trignometry
yes, good job
September 29, 2014

Pre-Calculus/Trignometry
Not totally familiar with the terminology of [2, infinity] , don't know if the 2 is included or not If the 2 in included, how about f(x) = √(x-2) if the 2 is excluded, we would use something like f(x) = 5/√(x-2)
September 29, 2014

math
number of dimes --- x number of quarters -- x-25 10x + 25(x-25) = 1650 10x + 25x - 625 = 1650 35x = 2275 x = 65 So 65 dimes and 40 quarters. check: 65 dimes = $6.50 40 quarters = $10 total = 16.50
September 29, 2014

Math Help
you have to learn to recognize the patterns. It looks like the primary function is 4/(something)^2 so let f(x) = 4/x^2 Now I see that instead of x in the denominator , I see 5x+2 so I let g(x) = 5x+2 so f(x) = 4/x^2 and g(x) = 5x+2 check: suppose we find f(g(x)) = f(5x+2) = 4...
September 29, 2014

math
So you were financing $5500 for 48 months with a monthly payment of $165.51 let the monthly interest rate be i 165.51( 1 - (1+i)^-48 )/i = 5500 This type of equation is very difficult to solve. In the "olden days" we used methods such as interpolation to get ...
September 29, 2014

Algebra
5x^3 . 2x^2 - 10x^4 + 3x^5 + 3x .(-2)x^4 = 10x^5 - 10x^4 + 3x^5 - 6x^5 = 7x^5 - 10x^4 The word "solve" is usually used when dealing with equations, that is, we solve an equation. You did not have an equation, so the instructions would be to "simplify" the ...
September 28, 2014

Calculus
change y = 2^x to ln y = x ln2 now take derivative: dy/dx / y = ln 2 dy/dx = y ln2 = ln2 (2^x)
September 28, 2014

math
number of children --- c number of adults ---- 155-c 5.3c + 8.7(155-c) = 1137.7 5.3c + 1348.5 - 8.7c = 1137.7 -3.4c = -210.8 c = 62 So 62 children tickets were sold on Friday
September 28, 2014

Pages: <<Prev | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | Next>>

Search
Members