Monday

May 30, 2016
Total # Posts: 40,888

**math**

since (a-b)^2 = a^2-2ab+b^2, just divide the middle coefficient by 2 and square it. (9/2)^2 and 5^2
*April 21, 2016*

**geometry**

see the related questions. Same problem, different numbers.
*April 21, 2016*

**Math**

x+y = 19 (x+5)(y+5) = 208 now just solve for x and y.
*April 21, 2016*

**Math- PLEASE HELP**

using the fact that the acute angles of right triangles are complementary, and that vertical angles are equal, it's pretty easy to determine that HXZ is 31°
*April 21, 2016*

**math**

v = s^3 dv/dt = 3s^2 ds/dt so, 3s^2 ds/dt = 5/2 as you can see, the rate of change of the sides depends on the size of the cube.
*April 21, 2016*

**math**

v = 4π/3 r^3 dv/dt = 4π r^2 dr/dt when r=5, dv/dt = 4π * 25 * 1 = 100π cm^3/s
*April 21, 2016*

**Math**

those logs are just numbers, so x log19 - 5log19 = x log3 + 2log3 x(log19-log3) = 2log3 + 5log19 x = 2log3 + 5log19 -------------------- log19 - log3
*April 21, 2016*

**Math/Precal**

2(3^x) = 5 3^x = 5/2 x log3 = log(5/2) x = log(5/2) / log3
*April 21, 2016*

**math- pre calc**

or, in QII, x = -12/13
*April 21, 2016*

**Math**

http://www.wolframalpha.com/input/?i=y%3D3x%2B1 any function of the form y=mx+b where m and b are numbers, is just a straight line.
*April 21, 2016*

**Grammar**

#1 is better, but it's kind of useless. Of course usefulness is valuable, or it would not be useful. I can think of a context where #2 is syntactically correct, but it's kind of weird.
*April 21, 2016*

**Chemistry - Answer Check**

looks good to me.
*April 21, 2016*

**probability**

ok - now what?
*April 21, 2016*

**math**

EF = 3*BC = 18
*April 21, 2016*

**Math**

for that person and that speed, c(t) = 420t if the other factors are variable, then you need a more general function including weight and speed: c(w,s,t) no idea what that would look like, but c(154,15,t) = 420t
*April 21, 2016*

**math**

since y increases in steps of 3, the rule will be something like y = 3x + b
*April 21, 2016*

**Precalculs**

one way: Ax=B, so you want A^-1 so that x = A^-1 B A = (1 2 3) (-1 2 -1) (-1 1 -2) B = (7) (1) (-2) A^-1 = 1/2 * (3 -7 8) (1 -1 2) (-1 3 -4) Now if you supply the missing value in B, you can do the multiply and get (-1 1 2), the solution. http://www.wolframalpha.com/input/?i=...
*April 21, 2016*

**math**

15 <= 2.54W <= 17 9 <= 2.54L <= 11
*April 21, 2016*

**Precalculs**

one way: Ax=B, so you want A^-1 so that x = A^-1 B A = (1 2 3) (-1 2 -1) (-1 1 -2) B = (7) (?) (-2) A^-1 = 1/2 * (3 -7 8) (1 -1 2) (-1 3 -4) Now if you supply the missing value in B, you can do the multiply and get (x y z), the solution. Or, you can do row operations as in ...
*April 21, 2016*

**Algebra**

a+b+c = 54 c = a+b-4 3a = c+4 now start substituting to solve
*April 21, 2016*

**mathe**

that's a strange shaped Egyptian, but assuming he is pyramidal in shape, the height h is found using h^2 = (100/2)^2-50^2 huh? If the sides have a slant height of half the base width, the pyramid is totally flat!
*April 21, 2016*

**math**

V = H*W*L just multiply the dimensions. the result will be in units of m^3.
*April 21, 2016*

**Math**

I think C is farther out than D.
*April 21, 2016*

**Pre-Calc**

review your basic trig functions, and you will that the height h (in miles) can be found using h cotx - h coty = 3
*April 21, 2016*

**sequences and Series**

or check the related questions, where it has been solved.
*April 21, 2016*

**maths**

The amount donated starts at 10, then grows by 6 each week. So, the donated amounts are 10,16,22,28,... So, the donated amount for the nth week is an arithmetic progression with a = 10, d=6 The total donations in 20 weeks is thus S20 = 20/2 (2*10 + 19*6) = 1340 Add that to the...
*April 21, 2016*

**Ratios!!!!**

#8 2x+3x+4x = 63 x = 7 So, the actual quantities are 14:21:28 #9 3ab/27ab = 1/9 So, A,B,E are the equivalent ratios. D doesn't get rid of the a,b stuff. Odd how you could get B and E right, but miss A and pick D... #10 B and D only
*April 21, 2016*

**math**

you are correct
*April 21, 2016*

**math**

1C is correct
*April 21, 2016*

**Math**

Reiny did this already at http://www.jiskha.com/display.cgi?id=1461201861
*April 21, 2016*

**Math**

organize things a bit better y = 3x^2+4x-8 y = 2x^2+4x-3 so, 3x^2+4x-8 = 2x^2+4x-3 x^2-5 = 0 x = ±√5 now use that to find y.
*April 21, 2016*

**Dosage calculations**

since the rate is 125ml/hr, why does it say 150 ml/hr? Anyway, your calculations look good. but watch the units. 1000ml/8hr = 125 ml/hr, not 125ml 125ml/hr * 3hr = 375ml
*April 20, 2016*

**Math**

6C4 .4^4 .6^2 = 0.138
*April 20, 2016*

**math**

after t years, p(t) = 23000 * 1.025^(t/8) so, p(25) = 24845 p(-10) = 22301
*April 20, 2016*

**Math**

dp/dt = -.06p dp/p = -.06 dt lnp = -.06t p = c e^(-.06t) where c is the starting value.
*April 20, 2016*

**Math**

your complex number is garbled.
*April 20, 2016*

**Math**

sine the rate of decrease is 14% of the amount present, dp/dt = -.14p dp/p = -.14 dt lnp = -.14t + c p = c e^-.14t here, c is the original amount when is only .22 left? e^-.14t = .22 -.14t = ln.22 t = ln.22/-.14 = 10.8 years
*April 20, 2016*

**Geometry**

well, I don't have a diagram, but if the pentagonal shape is just a rectangle with a triangle on top, its area is 8.5 * 17 + 1/2 * 17 * √(12^2-8.5^2) = 216.5 in^2 The round pizza has an area of 49π = 153.9 in^2 So, the cost of the home-plate pizza should be $10....
*April 20, 2016*

**Math**

Not sure what that description means, but if it is a cylinder atop a cone of radius 5 and height 4, then its volume is π/3 * 5^2 * 4 + π * 5^2 * 2 = 250π/3 So, the bottom cone must have the same volume: π/3 * 6^2 h = 250π/3 36h = 250 h = 250/36 = 6.9 cm
*April 20, 2016*

**math log rules / chemistry**

picking up where you left off, and fixing the minus sign you lost, (E2-E1)/0.05916 = -log[F+S] + log[F] (E2-E1)/0.05916 = log(F/[F+S]) 10^[(E2-E1)/0.05916] = F/(F+S) 10^[(E2-E1)/0.05916]F + 10^[(E2-E1)/0.05916]S = F F = 10^[(E2-E1)/0.05916]S ------------------------------ (1-...
*April 20, 2016*

**help azap**

length is ft area is length*width = ft*ft = ft^2 volume is length*width*height = ft*ft*ft = ft^3
*April 20, 2016*

**Statistics**

play around with Z table stuff here: http://davidmlane.com/hyperstat/z_table.html
*April 20, 2016*

**math**

no solutions. |x+1| is never negative, so adding 6 can never give a sum of 3. trick question.
*April 20, 2016*

**math**

180/x = tan 27°
*April 20, 2016*

**Maths**

review the basic trig functions. You will see that if the height is h, h cot13.5° - h cot 14.8° = 100
*April 20, 2016*

**Further maths**

just use what you know about AP's and GP's: (a+2d)/a = (a+8d)/(a+2d) a+6d = 14 AP: 2,4,6,8,... GP: 2,6,18,... Now you can easily find terms and sums.
*April 20, 2016*

**mathematics-abstract equations**

You know they are all perfect squares 64,81,9
*April 20, 2016*

**Math**

The trend will be positive, but depending on the age range, it may or may not look linear.
*April 20, 2016*

**Math**

assuming you meant a 10-ft ladder, then the height is √(10^2-2^2) = √96 If not 10, then fix it and use the same formula.
*April 20, 2016*

**Math**

0.42
*April 20, 2016*

**Analytic Geometry**

the major axis is vertical, so we have center: (0,0) a=13, b=12 c^2 = a^2-b^2, so c=5 vertices: (0,±13) covertices: (±12,0) foci: (0,±5) eccentricity e = c/a = 5/13 length of latus rectum is 2b^2/a = 2*144/13, so the latera recti are the lines through the ...
*April 20, 2016*

**math**

that's rubbish. Just typing in ellipse, I got many hits, and as usual, wikipedia had a very good article. https://en.wikipedia.org/wiki/Ellipse
*April 20, 2016*

**math**

depends on the conic section. google is your friend. Just look up "parabola" or "ellipse" etc for many discussions of their properties.
*April 20, 2016*

**Calculus**

-170 = -32t now, s = 16t^2
*April 20, 2016*

**Analytic Geometry**

well, you have a=5,b=3, so c=4. Now you can use that to proceed.
*April 20, 2016*

**math**

well, the difference d = (50-29)/(16-9) = 3 T20 = T16 + 4d ...
*April 20, 2016*

**math**

clearly, 2 3/4 + 3 1/3 miles
*April 20, 2016*

**Math**

since 1 cup is 3 times as much as 1/3 cup, she will need 3 times 4/5 c of flour.
*April 20, 2016*

**math**

3/4 * x = 2/5 (380-x) + 32 x = 160 Kelvin gets 160, spends 120 Winnie gets 220, spends 88
*April 20, 2016*

**Maths**

12000L / (150L/min) = 80 min
*April 20, 2016*

**Maths**

yes. That is the way they are defined.
*April 20, 2016*

**Calculus (easy)**

(2√2,5π/4)
*April 20, 2016*

**Calculus**

(i) v = ∫[0,1] π(R^2-r^2) dy where R^2=2-y^2 and r=y^2 (ii) v = ∫[0,1] 2πrh dy where r=y and h=√(2-y^2)-y^2
*April 20, 2016*

**science**

To conserve water, an animal's kidneys can pump ions across cell membranes, allowing water to move by
*April 19, 2016*

**Trigonometry**

well, since tan60° = √3, 2θ-34 = 60
*April 19, 2016*

**trig**

to find A, sinA/63 = sin53°/50 having C and A, B is easy since A+B+C=180. get b using law of sines or law of cosines.
*April 19, 2016*

**Polar, Cylindrical, and Spherical Coordinates**

good. I thought it would make sense if you looked at it a while.
*April 19, 2016*

**Polar, Cylindrical, and Spherical Coordinates**

no help from my earlier comments? http://www.jiskha.com/display.cgi?id=1461018078
*April 19, 2016*

**math**

15 km
*April 19, 2016*

**Math**

20/(3 1/2) = 20/(7/2) = 20*2/7 = 40/7 = 5 5/7 so, 5 pieces, plus 5/7 of a piece left over. Since one piece is 7/2 feet, 5/7 * 7/2 = 5/2 = 2 1/2 feet left over. Or, 20 - 5(3 1/2) = 20 - 17 1/2 = 2 1/2 ft left over
*April 19, 2016*

**Math**

if there are x liters of 25% juice, then there are (20-x) of 55% juice. So, .25x + .55(20-x) = .21(20)
*April 19, 2016*

**geometry**

with θ in radians, rθ = 8/5 since c=12, r = 12/(2π) = 6/π θ = (8/5)(π/6) = 4π/15 = 48°
*April 19, 2016*

**Algebra. NEED HELP ASAP PLEASE**

what is x when y=0? the intercept indicates how long it will take for sales of such cell phones to stop.
*April 19, 2016*

**math**

2^16 = 65536
*April 19, 2016*

**Calculus**

clearly e^(-6/√n) -> e^(-6/∞) = e^0 = 1
*April 19, 2016*

**Pre-Calc**

clearly -1 is not a solution, since log(-1) is not real. log3(x(x-2)) = 1 x^2-2x = 3 x^2-2x-3 = 0 (x-3)(x+1) = 0 so, yes, x=3 is a solution, but -1 is extraneous.
*April 19, 2016*

**math**

At distance x, the shadow has length s, so s/6 = (s+x)/8 s/6 = s/8 + x/8 4s = 3s+3x s = 3x ds/dt = 3 dx/dt so, the length of the shadow shrinks at a constant rate of 9 ft/s.
*April 19, 2016*

**geomtry**

have to know the linear scale. Areas scale by that value squared.
*April 19, 2016*

**math**

clearly, also 97 all the other prime factors must be less than 97, since they are factors of numbers from 1 to 96.
*April 19, 2016*

**math**

20 x^2 y But I suspect a typo.
*April 19, 2016*

**Geometry**

since AB=AC, ABC is isosceles, and AN, besides being an altitude, is another median, like CM. The medians intersect 2/3 of the way from each vertex to the opposite side. The altitude AN forms two 5-12-13 right triangles, so AN=12, and AX=8.
*April 19, 2016*

**Algebra**

Since there are two = signs, I'll assume the second one is a +. Then we have 7 – 5(2 – x) = –(x – 8) + 11/6 7 - 10 + 5x = -x + 8 + 11/6 5x+x = 8 + 11/6 - 7 + 10 6x = 77/6 x = 77/36 I expect there's a typo I misread, so just fix it and then follow ...
*April 19, 2016*

**math**

w(5w-23) = 42 Now solve for w. Or, consider that two factors of 42 are 6 and 7.
*April 19, 2016*

**Math**

since the angles add to 180°, angle F is 72°. Using the law of sines, DF/sin72° = 24/sin45° x = 32.28 So, did you just guess at A?
*April 19, 2016*

**Math**

-4+12 /(-3) 10+3(-2) -4 -4 10 - 6 I suspect another symbol is missing: ...(-3) ? 10 ... Maybe also after the +12 If so, fill it in and continue.
*April 19, 2016*

**Math**

or, once you have A and C, B = 180-(A+C)
*April 19, 2016*

**Math**

tan(θ)/ sec(θ) − cos(θ) = tanθ * cosθ - cosθ = sinθ/cosθ * cosθ - cosθ = sinθ - cosθ
*April 19, 2016*

**math algebra**

1.05x = 18165
*April 19, 2016*

**Math**

57 = 3s
*April 19, 2016*

**Algebra**

no, 45 = 9*5 9! = 9*8*7*6*5*4*3*2*1 = 362880 How ever did you decide on A?
*April 19, 2016*

**Math**

rubbish There's a 25% chance of not growing. So, P(3 not) = 7C3 .25^3 .75^4 = 0.17
*April 19, 2016*

**Further maths**

a = 3d d = 8 so, a=24 and the AP is 24,32,40,...
*April 19, 2016*

**Physics**

recall that F = k(q1 q2)/d^2 now just plug and chug, after looking up k.
*April 19, 2016*

**Math**

d = 40074/pi
*April 19, 2016*

**Math**

I don't see a question, but the expected value E = 3(3/34) + 2(10/34) - 1(21/34) = 4/17 = $0.24
*April 19, 2016*

**Calculus**

there are many handy Riemann um calculators online, such as http://www.emathhelp.net/calculators/calculus-2/riemann-sum-calculator/
*April 19, 2016*

**Calculus (Urgent, please)**

The curves intersect at (±1.25,1.56) using symmetry, the area is a = 2∫[0,1.25] √(4-x^2) - x^2 dx = 3.35
*April 19, 2016*

**Math**

7/10 + 7/20 = 21/20 So, 1/20 prefer both. But how can someone prefer two days?
*April 19, 2016*