Friday
July 1, 2016

Posts by Reiny

Total # Posts: 35,112

math
Interest = 100,000(.06)(30) = 180,000 (This is a completely meaningless answer. Nobody would charge simple interest for such a period of time. The formula assumes that there is always 100,000 owing, but aren't there payments made in a "house loan", generally ...
April 26, 2016

PreCal
I am missing the speed of the wind.
April 26, 2016

PRECALC
#1, look how I did this similar problem, and follow the same steps http://www.jiskha.com/display.cgi?id=1461697741 #2 2 cos(θ) tan(θ) + tan(θ) = 1 + 2 cos(θ) 2cosθtanθ - 2cos + tanθ - 1 = 0 2cosθ(tanθ - 1) + (tanθ -1) = 0 by ...
April 26, 2016

mathh
y - 67/36 = (1/4)(x - 4/9) expand, then multiply each term by 36, the LCD
April 26, 2016

precalc
square both sides cos^2 x + 2sinxcosx + sin^2 x = 1 1 + 2sinxcosx = 1 sin (2x) = 0 2x = 0 or 2x = π or 2x = 2π x = 0, x = π/2, x = π the period of sin 2x is π, so adding multiples of π will yield more answers so in the domain 0 < x < 2π...
April 26, 2016

Calculus
let the height of the water be h m let the radius of the water level be r m Make a sketch of the cross-section. By similar triangles: r/h = 40/10 r = 4h or h = r/4 V = (1/3)π r^2 h = (1/3)π(4h)^2 h = (16/3)π h^3 dV/dt = 16π h^2 dh/dt plug in the given ...
April 26, 2016

Math
What is 22,000(.94)^6 ??
April 26, 2016

Calculus
V = (4/3)πr^3 dV/dt = 4πr^2 dr/dt when r = 5 and dr/dt = 2 dV/dt = 4π(25)(2) = 200π cm^3/min SA = 4πr^2 d(SA)/dt = 8πr dr/dt = 8π(5)(2) = 80π cm^2/min
April 26, 2016

Geometry
Remember that for each chord , a perpendicular from the centre will right-bisect the chord so if you let the height to the shorter chord be h1, and the height form the centre to the longer chord be h2 you have two right-angled triangles, the first one sides 6, h1, and ...
April 26, 2016

maths
Look carefully, Damon had .75 not 75 45 minutes = 3/4 hour = .75 hours
April 26, 2016

Mathematics
number of boys --- x number of girls --- x+36 x/(x+36) = 2/5 5x = 2x + 72 3x = 72 x = 24 so we have 24 boys and 60 girls for a total of 84 adults/children = 5/6 adults/84 = 5/6 6adults = 420 adults = 70 All is known
April 25, 2016

Math
Prob = (1/2)(1/2)(1/2) = 1/8
April 25, 2016

Math
Since we can only add "like" terms, wouldn't we have to add x^3 + 5x^3 ?? And that would give us ..... ?
April 25, 2016

Math PLZZZ HELP ME!!!!!
look back at your previous post of this question.
April 25, 2016

Algebra
x^2+6x=-7 x^2 + 6x + 9 = -7+ 9 (x+3)^2 = 2 x+3 = ± √2 x = -3 ± √2
April 25, 2016

Math
The mathematical probability of rolling a 5 on a die is 1/6 so the number of times you would get a 5 in 300 rolls = (1/6)(300) = 50 so your "experimental" probability had to be different from the mathematical one. And you didn't state the experiment, so I can'...
April 25, 2016

Math
Let me try to wade through this quagmire of a sentence. A four digit decimal number lies between 10 and 20. ---> 1x.yz My tenths digit is twice my tens digit. ---> 1x.2z The sum of my tenths and my ones digit equals my hundredth digit. ---> 2+x=z ** The sum of all my ...
April 25, 2016

Math(Quadratic Functions)
For days ???? since the x-intercepts of a function are the same as the roots of the corresponding equation x=7 ----> a factor of (x-7) x=-2 ---> a factor of (x+2) so f(x) = a(x-7)(x+2) we are told that (0,5) lies on it, so 5 = a(-7)(2) a = -5/14 f(x) = (-5/14)(x-7)(x+2) ...
April 25, 2016

Roots, complex numbers
This question must be a popular one. Did it yesterday http://www.jiskha.com/display.cgi?id=1461490844
April 25, 2016

Math
A = 800(3)^3.12 = appr 24644 bacteria
April 25, 2016

Math
90000 = 45000(1.075)^n 2 = 1.075^n log both sides log 2 = nlog1.075 n = log2/log1.075 = appr 8.58 years
April 25, 2016

Calculus
let the height along the wall be y m let the distance from the wall along the ground be x x^2 + y^2 = 6^2 2x dx/dt + 2y dy/dt = 0 x dx/dt + y dy/dt = 0 when x = 4 16 + y^2 = 36 y = √20 , and dx/dt = 1 4(1) + √20 dy/dt = 0 dy/dt = -4/√20 m/sec the negative ...
April 25, 2016

algebra 2
see this similar question http://www.jiskha.com/display.cgi?id=1461613740
April 25, 2016

algebra 2
see this similar question http://www.jiskha.com/display.cgi?id=1461613740
April 25, 2016

math
volume = πr^2 h = π(25)(10) cm^3 = appr 785.4 cm^3 by the beauty of the metric system, that would be .7854 kg of water so the empty container weighs 2 - .7854 or aprr 1.21 kg
April 25, 2016

algebra 2
follow the same steps I just showed you in your previous post
April 25, 2016

algebra 2
you will need to find the vertex of this parabola, a) and c) can then be answered the t of the vertex is -b/(2a) = -64/-32 = 2 s(2) -16(4) + 64(2) + 80 = 144 the vertex is (2,144), what does that vertex tell you? b) when it reaches the ground, s = 0 -16t^2 + 64t + 80 = 0 ...
April 25, 2016

Math/Precsl
log(8y+12)=2 <-----> 8y + 12 = 10^2 8y = 88 y = 11
April 25, 2016

math
number of 100 rupee winners ---- x number of 25 rupee winners --- 63-x 100x + 25(63-x) = 3000 100x + 1575 - 25x = 3000 75x = 1425 x = 19 state your conclusion
April 25, 2016

Math
amount at 3% --- x amount at 8% --- 9000-x .03x + .08(9000-x) = 580 solve for x
April 25, 2016

geometric sequences
to find r, (90/17) / 9 = 10/17 and (900/289) / (90/17) = 10/17 a = 9 r = 10/17 term(n) = 9(10/17)^(n-1) term(10) = 9(10/17)^9 = appr .07589
April 25, 2016

Math/precal
for the y-intercept, let x = 0 y = 7b^0 = 7 for the x-intercept, let y = 0 0 = 7b^x no solution for x (normally we would take the log of both sides, but we can't take log0)
April 25, 2016

Maths
a + ar = 9 a(1+r) = 9 a = 9/(1+r) a/(1-r) = 12 a = 12(1-r) 12(1-r) = 9/(1+r) 1 - r^2 = 3/4 4 - r^2 = 3 -r^2 = -1 r = ± 1
April 25, 2016

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

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