Tuesday
May 24, 2016

Posts by Reiny

Total # Posts: 34,779

maths
Just add them, the 1/y's will drop out 2/x = 6 6x = 2 x = 1/3 sub into the original first 1/y + 1/(1/3) = 5 1/y + 3 = 5 1/y = 2 y = 1/2
April 25, 2016

Math
For the volume I got 538.8 ft^3 to the nearest tenth of a foot. (you should really use a better value for π than 3.14, most calculators have it built in correct to 10 decimals) Your SA is made up of 2 circles + a rectangle SA = 2π(3.5)^2 + 2π(3.5) = 384.8 ft^2
April 25, 2016

Algebra
Where does the 4 come from? There are 36 cookies in 6 bags, so the number of cookies in each bag = 36/6 = 6
April 25, 2016

Calculus
let the length of line be L ft let the horizontal distance of the boat from the dock be x ft You have a right-angled triangle, thus x^2 + 3^2 = L^2 2x dx/dt = 2L dL/dt for the given case: x = 4 L^2 = 4^2 + 3^2 L = 5 2(4)(7) = 2L dL/dt dL/dt = 2(5)/(56) = 5/28 ft/s
April 25, 2016

MATH
What am I missing here? Isn't the circumference of the cylinder simply the circumference of the circle? which would be 3.2π inches. The height of 8 inches would have nothing to do with it.
April 25, 2016

Math
volume of cubes is proportioanl to the cube of their corresponding sides so V/729 = 4^3/3^3 27V = 46656 V = 1728 notice the sides increased by a ratio of 4:3 and 1728/729 = 64/27 = 4^3 : 3^3
April 25, 2016

Algebra
Ok, multiply the first by 4, then subtract the 2nd multiply the first by 3, then subtract the third. Now you have two equations with y's and z's carry on
April 25, 2016

Algebra
Why eliminate x when the obvious choice would be to eliminate z ?? #2 - #1 ---> 3x - 4y = 1 ** #2 - #3 ---> x - y = 2 or x = y+2 sub that into ** 3(y+2) - 4y = 1 3y + 6 - 4y = 1 -y = -5 y = 5 , then x = 7 back into #1: 7 + 5 + 5z = 2 5z = -10 z = -2 so the solution is (7...
April 25, 2016

Maths
2nd term = a+d 7th term = a+6d a+d + a+6d = 20 2a + 7d = 20 ** (a+d)/(a+6d) = 1/3 3a + 3d = a + 6d 2a = 3d *** sub that into ** 3d + 7d = 20 10d = 20 d = 2 then 2a = 6 a = 3 "Calculate The Sum Of The 1st Terms Of The G.P" HUH? I thought we were dealing with an AP. ...
April 25, 2016

algebra
short leg --- x longer leg --- x+2 x^2 + (x+2)^2 = 8^2 x^2 + x^2 + 4x + 4 - 64 = 0 2x^2 + 4x - 60 = 0 x^2 + 2x - 30 = 0 let's complete the square: x^2 + 2x + 1 = 30+1 = 31 (x+1)^2 = 31 x+1 = ± √31 x = -1 ± √31 but x has to be positive, so x = &#...
April 24, 2016

Math
take 1/2 of the -7 and square that so (-7/2)^2 = 49/4 we should add 49/4 to both sides
April 24, 2016

Math
herding my way through that first "sentence" .... I got the obvious: h = -16t^2 + 96t + 3 a) plug in t = 0 b) find the vertex and both b) and c) are answered.
April 24, 2016

Math
what is 7! ?
April 24, 2016

Math
That's a lot of fencing.. No diagram can be used in this format. Check your post for typos and grammar before posting.
April 24, 2016

Math
3 -> 9 5 -> 25 2 -> ? 7 -> 49 if x is input and y is output, it sure looks like y = x^2
April 24, 2016

Math
prob(all 4 boys) = (1/4)^4 = 1/256 = .... you do the button-pushing
April 24, 2016

Algebra 1
No, your choice is not correct It is B If I multiply the first equation by -2, don't I get the 2nd equation??? So one is a multiple of the other.
April 24, 2016

Algebra 1
let's look at the 2nd equation. −2x − 6y = 2 multiply by -1 2x + 6y = -2 divide by 2 x + 3y = -1 , well, isn't that the first equation??? So, do you want to change your choice?
April 24, 2016

Math
the diameter of the large cookie is 4 times that of the smaller cookie. The area is proportional to the square of their diameter, (or their radii) so the larger one is 16 times the area, thus it should cost 16 times the smaller, or 80 cents. B would be my choice.
April 24, 2016

Math
you are right
April 24, 2016

Algebra
I will assume from looking at the answers that you meant y = √(3x+3) Since we only take √'s of non-negative numbers, 3x+3 ≥ 0 3x ≥ -3 x ≥ -1
April 24, 2016

calculus
I would simplify it first f(x) = 1 + 9/x - 3/x^2 f ' (x) = -9/x^2 + 6/x^3 = 0 for a max/min 6/x^3 = 9/x^2 9x^3= 6x^2 9x^3 - 6x^2 = 0 3x^2(3x - 2) = 0 x = 0 , but that would make f(x) undefined, or x = 3/2 f(3/2) = 1 + 9/(3/2) - 3/(9/4) = 1 + 6 - 4/3 = 17/3
April 24, 2016

calculus
f(x) = 2x(x-1)^(-1/2) f ' (x) = 2x(-1/2)(x-1)^(-3/2) + 2(x-1)^(-1/2) = 0 for critical values, (max/mins) x/(x-1)^(3/2) = 2/(x-1)^(1/2) times (x-1)^(3/2) x = 2(x-1) x = 2x - 2 x = 2 f(2) = 4/sqrt(1) = 4 the critical number, in this case a minimum is (2,4)
April 24, 2016

Anti-Derivatives
distance = -16t^2 + h velocity = -32t but we know that is -170 so -32t = -170 t = 85/16 seconds so how far his it fallen in 85/16 seconds? distance = 16(85/16)^2 = 7225/16 ft or appr 451.56 ft
April 24, 2016

Algebra
original amount -- x x - (x/8 + x/5 + x/10) = 15 x - 17x/40 = 15 40x - 17x = 600 23x = 600 x = 26.09 , correct to 2 decimals
April 24, 2016

Math
what is 270/450 ?
April 24, 2016

math
ar^2 + ar^3 = -4/3 ar^2(1 + r) = -4/3 ** ar^3 + ar^4 = -4/9 ar^3(1 + r) = -4/9 *** divide *** by ** ar^3(1+r)/(ar^2(1+r)) = (-4/9) / (-4/3) r = 1/3 plug back into ** a(1/3)^2 (1 + 1/3) = -4/3 a(1/9)(4/3) = -4/3 a = -9 term(6) = ar^5 = -9(1/3)^5 = -1/27 check: sequence is: -9...
April 24, 2016

math
done here http://www.jiskha.com/display.cgi?id=1461503265
April 24, 2016

Maths
what is 20 - (2/5)(20) - (1/5)(20) ? or they ate 3/5 of your chocs so you have 2/5 of 20 left
April 24, 2016

math
P = k L^2 when P=108, L=6 108 = 36K k = 3 P = 3L^2 75 = 3L^2 L^2 = 25 L = 5
April 24, 2016

math
you are choosing all possible pairs from 40 to shake hands, that would be C(40,2) = 780 or think of it this way: each of the 40 people can shake hands with 39 other people which is 40x39 = 1560. BUT, that includes identical pairs, e.g. A shaking with B is the same as B shaking...
April 24, 2016

math
Your Taylor expansion of f(x) is correct I disagree with your derivative, it should be (-1/4)((1/16 + x)^(-5/4) why not just integrate ʃ(1/16 +x)^(-1/4) dx to get (4/3)(1/16 + x)^(3/4) + C
April 24, 2016

maths
let z^5 = rcosθ + rsinθ i = -1 + 0 we have r = 1 θ = 180° so z^5 = 1(cos180° + isin180°) by de Moivre's theorme z = 1^(1/5)(cos 180/5 + i sin180/5) = 1(cos 36° + isin36°) or cis36° repeating at 360/5 or 72° z = cis 36° z = ...
April 24, 2016

math
(3.3x10^3)(1.8x10^4) = 5.94 x 10^7
April 23, 2016

Math
the prob that the biased coin is tails = .4 so prob(3tails) = .4^3 = .064 So what do you think?
April 23, 2016

Pre-Calc
we can only take logs of positive numbers so 3x-8 > 0 3x > 8 x > 8/3 I will let you write it in the new-fangled notation. In my time we used the above simple way of stating it.
April 23, 2016

maths
x^3 + y^3 = 72 x^2 - y^2 = 12 We could just do this by listing the cubes less than 72 : 1, 8, 27, 64 the only combination for a sum of 72 is 8 + 64 so x=2, y=4 so the numbers are 2 and 4 is the difference property ok? is 16-4 = 12 ?? YES
April 23, 2016

math
the largest prime < 50 is 47 the smallest composite > 10 is 12 so what is the difference between those ?
April 23, 2016

Math
s = t(t^2 - 8t + 16) = t^3 - 8t^2 + 16t v = 3t^2 - 16t + 16 a = 6t - 16 for zero of a, 6t-16=0 t = 16/6 = 8/3 seconds when t = 8/3 v = 3(64/9) - 16(8/3) + 16 = -16/3 s = (8/3)(8/3 - 4)^2 = 128/27 work these answers in with your concluding statements
April 23, 2016

maths
When it falls down, the distance is zero so 0 = 30t - 4.9t^2 t(30 - 4.9t) = 0 t = 0 , that would be at the beginning or t = 30/4.9 or appr. 6.12 seconds 2nd part: 20 = 30t - 4.9t^2 4.9t^2 - 30t + 20 = 0 t = (30 ± √508)/9.8 = .761 seconds, on its way up or = 5.36 ...
April 23, 2016

algebra
did you mean an = (3)^(n−1) ? if so, follow the same steps I showed you in your previous post.
April 23, 2016

sequence
If n = 1, term(1) = 4 if n = 2, term(2) = 8 if n = 3, term(3) = 12 etc
April 23, 2016

Math
Unless I see an obvious identity I can replace, I usually change everything to sines and cosines. LS = (1/cosx - cosx)/(sinx/cosx - sinx) = ( 1 - cos^2 x)/cosx )/( (sinx - sinxcosx)/cosx ) = ( 1 - cos^2 x)/cosx )* cosx/( (sinx - sinxcosx) = (1 - cos^2 x)/(sinx(1 - cosx)) = (1...
April 23, 2016

math
shares bought at RS140 --- x shares bought at RS125 --- y amount invested at 6% --- 140x amount invested at 5% --- 125y 140x + 125y = 6750 ** .06(140x) + .05(125y) = 280 8.4x + 6.25y = 280 times 20 168x + 125y = 5600 *** subtract ** from *** 28x = -1150 not possible. Unless ...
April 23, 2016

geomentry
I drew a line AB, with A to the left of B I marked P and Q on the left side of the midpoint. "Point P divides AB in the ratio 2:3" ---> let AP = 2x and PB = 3x then AB = 5x "Q divides AB in the ratio 3:4" --> let AQ = 3y and QB = 4y then AB = 7y ...
April 23, 2016

Maths
The altitude in an isosceles triangle right-bisects the base, so BD = DC let BD = x then BC = 2x AB = 4x in the right-triangle ABD AD^2 + x^2 = (4x)^2 = 16x^2 AD^2 = 15x^2 AD^2 = 15BD^2 , not 15 BC^2 as you stated.
April 23, 2016

Finance
amount at 4% compounded quarterly = 1500(1.01)^20 = .. amount at 4% compounded semi-annually = 1500(1.02)^10 = .. amount at 4% per annum = 1500(1.04)^5 = ...
April 23, 2016

Math
let the number be x x/2 + 4 = 10 carry on
April 22, 2016

Math, NEEDS HELP EMEDIETLY!
To me the method of your solution is much more important than the answer. Since your method makes no sense, it would benefit you to actually care more about how the answer is obtained. 7/12 of the students take martial arts, and (7/12)(144) = 84 sample size?? well, how many ...
April 22, 2016

Science/Math
a = -4 m/s^2 v = -4t + k when t = 0, v = 3- thus k = 30 v = -4t + 30 when the vehicle stops, v = 0 0 = -4t + 30 4t = 30 t = 30/4 or 7.5 seconds
April 22, 2016

Calculus Help
lim (5 - √x)/(x-25) as x ---> 25 = lim (5-√x)/((√x-5)(√x+5)) = lim -1/(√x+5) as x ---> 25 = -1/(5+5) = -1/10
April 22, 2016

math
√-1 , also called i , is a complex or imaginary number. Every other complex number can be expressed in terms of i
April 22, 2016

math
Your start would be to make a diagram of the right-angled triangle. Then you should see that if L is the length of the ladder, sin76° = 10/L L = 10/sin76° = 10.306 m
April 22, 2016

Mathematics
let u = e^x then u^2 = e^(2x) and du/dx = e^x dx = du/e^x = du/u ʃ e^x /sqrt[e^(2x) -1] dx = ʃ u/√(u^2 - 1) du/u = ʃ 1/√(u^2 - 1) du = ln (√(u^2 - 1) + u) , from my old integration formulas = ln((√(e^(2x) - 1) + e^x) + C
April 22, 2016

Geometry
circumference of whole circle = 2pi r = 6pi so : arc/6pi = 20/360 arc = 120pi/360 = pi/3 = appr 1.047 units or arc = rθ , where θ is the angle in radians so 20 degrees = 20pi/180 radians = pi/9 arc = 3(pi/9) = pi/3 , same as above
April 22, 2016

Math (Calculus)
Yes, it does work, let's set -6x^2+20.4x+202.275 = 0 6x^2 - 20.4x - 202.275 = 0 I used the formula and got x = 7.75 or x = -4.35 remember that the function is increasing when the derivative is postive, and decreasing when .... so the function is increasing for -4.35 < x...
April 21, 2016

Math Pythagorean
northern direction = 3 - 1 + 2 = 4 eastern direction = 2 + 4 = 6 h^2 = 4^2 + 6^2 = 52 the hypotenuse is √52 = appr. 7.2 miles
April 21, 2016

Math
older sister --- x younger sister --- 19-x in 5 years: (x+5)(24-x) = 208 -x^2 + 19x + 120 - 208 = 0 x^2 - 19x + 88 = 0 (x-11)(x-8) = 0 x = 11 or x = 8 older sis is 11, younger is 8 check: in 5 years: 16(13) = 208 , all is good
April 21, 2016

Math
expand: (x-5) log19= (x+2) log3 xlog19 - 5log19 = xlog3 + 2log3 xlog19 - xlog3 = 2log3 + 5log19 x(log19 - log3) = 2log3 + 5log10 x = (2log3 + 5log19)/(log19 - log3) = appr 9.1663
April 21, 2016

algebra 2
(21 − 4i) − (16 + 7i) + 28i just like basic algebra ... = 21 - 4i - 16 - 7i + 28i = 5 + 17i
April 21, 2016

math 1
8p^2 + 56p + 98 = 2(4p^2 + 28p + 49) = 2(2p + 7)^2 ----> notice the perfect square in the 2nd last line
April 21, 2016

Math
–1, 9, 19, 29, . . . looks like you are adding 10 each time, so the next 3 terms would be 39, 49, 59 None of your choices match that, unless C contains a typo Your choice of D is definitely wrong
April 21, 2016

Math- Check my answers please!
#3 4^4/4^6 = 1/4^2 = 1/16 #5 7^4/7^2 = 7^2 = 49 #6 –2r(8r + 5) = -16r^2 - 10r #7 4a(a^2 + 7a + 4) = 4a^3 + 28a^2 + 16a #8 (2y-3)(3y-2) = 6y^2 - 4y - 9y + 6 = 6y^2 - 13y + 6 Looks like somebody has some major review ahead of them.
April 21, 2016

maths-I only need the solution
To me, the actual solution is less important than the method of getting that solution. We should assume that all values would be whole numbers. More than that, all numbers would have to be perfect squares or else we would have decimals suppose we subtract the second from the ...
April 21, 2016

Math
What part of yesterdays solution did you not like? http://www.jiskha.com/display.cgi?id=1461201861
April 21, 2016

math0
We have to know how many gumballs there are and how many of each colour.
April 21, 2016

maths
P = k/Q + C given: P=3, Q=9 3 = k/9 + C 27 = K + 9C *** P=9, Q = 18 9 = k/18 + C 162 = k + 18C ** subtract *** from ** 135 = 9C C = 15 in *** k+135 = 27 k = -108 P = -108/Q + 15 so when Q = 12 P = -108/12 + 15 = 6
April 21, 2016

sequences and Series
I have now answered 6 of your questions without any effort on your part showing me that you have attempted these. What do you think about this one? Why not just follow the rules of the sequence as you stated them?
April 21, 2016

Maths
Ok so far simplify your expression a bit and use proper brackets = 11Ck (1/4)^(11-k) (-16)^k x^(11-k) y^k so y^k <----> y^4 thus k = 4 the coefficient comes from 11Ck (1/4)^(11-k) (-16)^k = 11C4 (1/4)^7 (-16)^4 = 330(1/16384)(65536) = 1320 confirmation: https://www....
April 21, 2016

sequences and Series
geeesh, why not just list the berries handed out for each house? There are only 5 identical steps
April 21, 2016

Sequences and Series
appears to go 6,5,1,2 ..... a cycle of 4 terms. the 21st term must be 6
April 21, 2016

Sequences and Series
add 1 to each even numbered term add 5 to each odd numbered term 25,5,30,6,35,7,40,8,45,...
April 21, 2016

Series and Sequences
Not enough data to tell for the first 3, there is an increase of 20 from one to the other for the last three, there is the same increase but we can't tell what happened from term3 to term4
April 21, 2016

please math help
T/F ---- x multiple choice --- y x+y = 20 ----> y = 20-x 3x + 11y = 100 3x + 11(20-x) = 100 3x + 220 - 11x = 100 -8x = -120 x = 15 and then y = 5 There are 5 multiple choice questions
April 21, 2016

Math linear equations
large pitcher --- x small pitcher --- y x + 2y = 8 x - y = 2 subtract them: 3y = 6 y = 2 then x = 4 large holds 4 cups, the smaller holds 2 cups
April 21, 2016

Math
radius of circle = 1450 ft circumference of whole track = 2π(1450) = 2900π ft angle of sector between them = 90 + arctan(1440/170) = 173.267° Distance Robin has to make up is 173.267/360 = x/2900π x = 4384.9155 ft He is gaining on him at a rate of 1.3 ft/sec...
April 20, 2016

Math
prob(grow) = .65 prob(not grow) = .35 prob(1 of 11 will not grow) = C(11,1)(.35)(.65)^10 = .05183
April 20, 2016

NEED HELP MATH QUESTION ASAP
Prob(rolling a two) = 1/6 number of expected times of getting a 2 in 6 rolls = 6(1/6) = 1
April 20, 2016

Math
I assume you meant:Volume = 4(c)^3(b)^8 Base area = 16(ab)^3 let the height be h h(16(ab)^3) = 64(c)^3(b)^8 h = 4 c^3 b^5 /a^3 No choice is correct
April 19, 2016

math
age of son ---- x age of woman --- 4x 5 years from now: son : x+5 woman : 4x+5 4x+5 = 3(x+5) solve for x
April 18, 2016

Trig
This same post has been declared as muddled and garbled several times. It has been answered by both Steve and I and you should not expect any more replies until you fix the wording so that the question makes sense http://www.jiskha.com/display.cgi?id=1460596777
April 18, 2016

Math/algebra
Cutting through the chase: 60 + -25x = 35x + 20 -25x - 35x = 20 - 60 -60x = -40 x = 40/60 = 2/3
April 18, 2016

Trigonometry
draw your triangles in the correct quadrantIs. Use Pythagoras in each case. if cosu = 3/5, in IV, then sinu = -4/5 if cosv = 12/13, then sinv = -5/13 sin(u-v) = sinu cosv - cosu sinv = (-4/5)(12/13) -(3/5)(-5/13) = (-48 + 15)/65 = -33/65
April 17, 2016

Ms Sue please helpp
4356/9999 = 484/1111
April 17, 2016

Algebra
x y 1stdiff -- 2nddiff 0 4 1 5 -- 1 ----- 2 8 -- 3 ----- 2 3 13 --5 ----- 2 4 20 --7 ----- 2 since the 2nd difference is a constant, it must be a quadratic, or 2nd degree function
April 15, 2016

Algebra
take 1/2 of the coefficient of the middle term, then square it, so c = 169/4
April 15, 2016

Algebra
rate of smaller pipe --- 1/x rate of larger pipe ---- 1/(x-18) , where x > 18 combined rate = (x-18 + x)/(x(x-18) = (2x-18)/(x^2 - 18x) 1/[(2x-18)/(x^2 - 18x)] = 12 x^2 - 18x = 24x - 216 x^2 - 42x + 216 = 0 (x - 36)(x - 6)= 0 x = 36 or x = 6 but x = 6 does not fall into my ...
April 15, 2016

Algebra
http://www.jiskha.com/display.cgi?id=1460741071
April 15, 2016

Algebra
look below at Related Questions for variations of your question. Simply change the numbers in the solution by Henry
April 15, 2016

Algebra
your equation should be s = -4t^2 - 6t + 100 you want to know when s = 0 4t^2 + 6t - 100 = 0 2t^2 + 3t - 50 = 0 t = (-3 ±√409)/4 = appr 4.3 seconds or a negative, which we will reject
April 15, 2016

Algebra
speed of slower plane --- x km/h speed of faster plane --- x+50 km/h 1400/x - 1000/(x+50) = 3 times x(x+50) 1400(x+50) - 1000x = 3x(x+50) 1400x + 70000 - 1000x = 3x^2+ 150x 3x^2 - 250x - 70000 = 0 (x - 200)(3x + 350) = 0 x = 200 or a negative, which is rejected The slower ...
April 15, 2016

math
In the first case I would be dividing both sides by -4 In the second equation I would be multiplying both sides by -4 the two answers differ by a factor of 16
April 15, 2016

math
you are welcome
April 15, 2016

math
From some starting point, draw 5 lines downwards. From the end of each of those lines, branch off 3 more lines each There should now be 15 endpoints.
April 15, 2016

maths
Confirming Steve's conclusion: https://www.wolframalpha.com/input/?i=Plot+y+%3D+e%5Ex,+y+%3D+x
April 15, 2016

engineering mathematics
let f(x) = x^3 - 6x^2 + 13x - 9 f'(x) = 3x^2 - 12x + 13 xnew = x - f(x)/f'(x) = x - (x^3 - 6x^2 + 13x - 9)/(3x^2 - 12x + 13) = (3x^3 - 12x^2 + 13x - x^3 + 6x^2 - 13x + 9)/(3x^2 - 12x + 13) = (2x^3 - 6x + 9)/(3x^2 - 12x + 13) using my calculator, with an initial guess ...
April 15, 2016

math
for a fun topic along these lines, Google and look into the "chinese remainder theorem"
April 14, 2016

math
So the number must be such that when divided by 3 , leaves a remainder of 1 when divided by 4 , leaves a remainder of 1 when divided by 5 , leaves a remainder of 1 Find the lowest common number is these sets: 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64..... 5 ...
April 14, 2016

algeabra
x+7 divided by x-4 = 1 + 11/(x-4) test by adding 1 + 11(x-4)
April 14, 2016

maths
Jake --- x Ken ---- 4x giveaway: Jake --- x+360 Ken ---- 4x-360 4x-360 >= x+360 3x >= 720 x >= 240 Ken >= 600 The least Ken will have is 600
April 14, 2016

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