Friday
May 29, 2015

Posts by Steve


Total # Posts: 31,439

Math
384/6 = 64 There are three terms, so r = 4 T6 = T4*r^2 = 6*16 = 96 r^3 = 8!/7! = 8 so, r=2 T1 = T5/r^4 = 7!/16 = 315
March 13, 2015

Statistics - Can anybody help me?
after t hours, starting with A mg, the amount remaining is A*.76^t So, to find the original dose, solve A*.76^5 = 74 To get to 25%, you want .76^t = .25
March 13, 2015

Steve - Stat
9.0508% 2250 * 1.0905077^33 = 39258 showing the proper growth rate. Maybe they don't want a percent, but a factor?
March 13, 2015

Math
128/32 = r^2 r=2, so y=32*2=64 Or, evaluate the logs. The sequence is thus 5,log2(y),7 so, log2(y) = 6, and y=64 log a^2b^3 = 2loga + 3logb log a/b = loga - logb 2loga + 3logb = x loga - logb = y 2loga + 3logb = x 2loga - 2logb = 2y 5logb = x-2y logb = (x-2y)/5 solve for loga ...
March 13, 2015

math
% means per 100, so 34.6% = 34.6/100 = 0.346
March 13, 2015

Stats - Please help me
Since it grows by a factor of 2 every 8 days, the population is 2250 * 2^(t/8) In 33 days there will be 39258 The growth factor for each day is 2^(1/8) = 1.0905, for a 9.05% per day growth rate
March 13, 2015

Science
well, it combines CO2 with H2O to make sugars, storing energy. When this happens, heat is absorbed to drive the reaction and store energy in the sugar molecules.
March 13, 2015

Check My Answers Math
#9 eh? t=9, so d = t/3 = 3 km How did you get 12? That's d = t+3 #10 Did you check your answer? Note that y increases by 15 for each x, and starts at 14. So, y = 14+15x #11 Oh, please. Do you just pick a letter and hope? The first two, maybe you were just careless. But ...
March 13, 2015

Algebra
.20x + .50(30-x) = .30(30) x=20 So, 20ml of 20% and 10ml of 50% Note that 30% is 1/3 of the way from 20% to 50%, so 1/3 of the acid is the higher concentration.
March 13, 2015

math
2/5 of the height of the cone is missing. The complete cone would have a slant height of 100. The lateral area of a cone is πrs, so what we have is π(35)(100) - π(14)(40) = 2940π The hemisphere has area 2πr^2 = 2π(35^2) = 2450π The bottom of ...
March 13, 2015

Pre ALGEBRA
Since 1(1-2)-3 = -4, (b) is certainly the only possible choice, since the others don't start with -4. Luckily, the other values also work, so (b) it is.
March 13, 2015

Pre ALGEBRA
add 11 each time. You are correct.
March 13, 2015

Math Check My Work Please
#?: y=2x+1, not 2x-1 #6: The sequence starts with n=1 #7: 3.60 * 18 = ?
March 13, 2015

math
no way to make a square out of 120 blocks If you had 121, the square would be 11x11. (so, you could make a square if you left the center block out)
March 13, 2015

Calculus 1
y = e^(4t sin2t) y' = e^(4t sin2t)(4sin2t + 8tcos2t)
March 13, 2015

Calculus 1
you can factor out the 2(2x+1)^4 (x^4-3)^5 and you have 2(2x+1)^4 (x^4-3)^5 (5(x^4-3) + 12x^3(2x+1)) = 2(2x+1)^4 (x^4-3)^5 (29x^4+12x^3-15)
March 13, 2015

maths
1.4 L/s * 28s = 39.2L = 39200 cm^3 so, the side is ∛39200
March 13, 2015

Math 2
6/x = cos 61°
March 13, 2015

vectors and geometry
correct. You didn't even have to find a+b.
March 13, 2015

INT. Algebra
since WV is constant, 63*9 = W*81
March 13, 2015

Math
#1: (4p-1)-(6p) = (p^2-1)-(4p-1) #2: (y+6)/3y = -3 y = -3/5 (z+1)/(y+6) = -3 Now plug in y and solve for z
March 13, 2015

Mathematics
a + a+d = 4 a+9d = 19 so, find a and d, and then you want a+4d + a+5d
March 13, 2015

Geometry
Pythagorus won't help here. Your ladder must reach up 26 ft. That means that the ladder's length x is given by 26/x = sin 68°
March 13, 2015

math
each equation must be of the form y = mx+b Since they are parallel, they all have the same slope. So, just pick any value for m, and write four equations using the same m, and different values for b. I assume you can graph such lines.
March 13, 2015

Math Triangles
google is your friend. Go to http://www.authorstream.com/Presentation/ramarao.velury-1400926-7similartriangles-rev1/ and skip to page 12. The problem is explained.
March 13, 2015

math
another way. You do not need to find k at all. You know that f = k/g, so fg = k, a constant. That means that 20*4 = f*10
March 12, 2015

factorise fully
rearrange a bit and you have px(p-2q) - qy(p-2q) (px-qy)(p-2q)
March 12, 2015

factorise fully
difference of cubes, so (5x-4y)((5x)^2+(5x)(4y)+(4y)^2) . . .
March 12, 2015

factorise fully
difference of squares, so ((a+b)+x)((a+b)-x) ...
March 12, 2015

Algebra
clearly you want y >= 0 -0.1x^2+12 >= 0
March 12, 2015

factorise fully
(a-2b)^2 - 16x^2 now you have a difference of squares (a-2b+4x)(a-2b-4x)
March 12, 2015

algebra
.08(21000) + .04x = .05(21000+x)
March 12, 2015

Love Math
(28/4).5-6 + 4^2 powers first. so (28/4)*5-6+16 Inside parens, (7)*5-6+16 Now no parens, 7*5-6+16 Now multiply, 35-6+16 Now add/subtract, left-to-right: 29+16 45
March 12, 2015

Algebra u rgent
Odd, how you got #2 ok, but got stuck on #1 x increases by 1, and y increases by 1, so the slope is 1/1 = 1
March 12, 2015

Math
You start by (a) noticing that you misspelled too (b) reviewing your text so you know what the different words mean: sum, product, term, etc. A sum is two terms separated by a + or - sign (a) 56xy + 5 is a sum 5 - 6x is a sum (b) Terms are separated by + and - signs. So, the ...
March 12, 2015

Math
the map circle has radius 2 in. So, that represents a land circle of radius 120 mi. So, what's the area of such a circle?
March 12, 2015

Math
well, you can surely see that you want the part in the first quadrant. Then you an consider the line 3x+2y=6 Obviously, any x or y less than what's on the line will satisfy the inequality. SO, you want the region below the line, in QI: http://www.wolframalpha.com/input/?i=...
March 12, 2015

geometry
The median from A goes to the midpoint of BC at (6,3) Its slope is 3/8, so its equation is y = 3/8 (x+2) The bisector of BC also goes through (6,3) with slope -2/5, so its equation is y-3 = -2/5 (x-6)
March 12, 2015

Math
5-2=3 2+3=5 so, which is greater, 3*3 or 2*5?
March 12, 2015

algebra--1 question
Neither. It is (x+3)(x+4) (x-3)(x-4) = x^2-7x+12 (x-3)(x+4) = x^2+x-12
March 12, 2015

Math
1 large bag is 2/(5/6) = 12/5 small bags So, 5 large bags = 12 small bags
March 12, 2015

Math
draw the road, and label the houses DM=4 MC=1 So, DC = DM+MC = 5 Randy does not matter in this calculation.
March 12, 2015

7th grade geometry
if the prism has dimensions x,y,z, then if each dimension is increased by 2.5, we have 2(xy+xz+yz) = 2((3.5+2.5)(1.5+2.5) + (3.5+2.5)(2+2.5) + (1.5+2.5)(2+2.5)) = 138 ft^2 But, I doubt that is what happens. The question now is, how wide is the paper, and which dimension(s) get...
March 12, 2015

algebra
Just use your distance formula: d^2 = (7+9)^2 + (-6-5)^2
March 12, 2015

periodic functions(math)
(a) see http://www.wolframalpha.com/input/?i=plot+2.5sin%280.523t%29%2B2.9+for+t%3D0+to+24 (b) since sin(kt) has period 2π/k, sin(.523t) has period 2π/.523 = 12.01 That is, the tide cycles every 12 hours. (c) look at the graph and see where d(t) >= 1.3 You want ...
March 12, 2015

Math
6b+3o = 10 3b+5o = 12 12b+6o = 20 9b+15o = 36 21b+21o = 56 b+o = 56/21 = 2.67
March 12, 2015

math
If she saves for n days, she will need n(n+1)/2 >= 7000
March 12, 2015

math
3C1 * 7C3 * 3C1 = 3*35*3
March 12, 2015

physics
.35 ton * 2000lb/ton * 1N/.2248lb = 3113.88 N
March 12, 2015

algebra
I find it helps to have the highest powers first: -2x^2+7x-6 -(2x^2-7x+6) -(2x-3)(x-2)
March 12, 2015

alg. Compounding periods.
#1) how many months in 5 years? #2) 11000(1+.035/365)^90 = 11095.34
March 12, 2015

math
the wheel has a diameter of 30 ft So, its circumference is 30π ft That means that 4 trips around = 4*30π = 120π ft
March 12, 2015

Math
Assuming the three angles are listed in order, you have to remember that consecutive angles are supplementary opposite angles are equal. So, 5x-2 + 8y+2 = 180 5x-2 = 3x+22 So, x = 12, making y=15
March 12, 2015

calc
Been there, done that. 1st related question below: http://www.jiskha.com/display.cgi?id=1425923355 Always check the related questions when you have posted one. Yes, it's not often easy to find the ones you want before.
March 12, 2015

linear equation and one variable
If the pencil costs x, then the pen costs 7x The rest of the posting makes no sense. I think you left out an amount somewhere.
March 12, 2015

Physics
v = √(1.8^2 + (9.8*3)^2) = 29.45 If θ is the angle from the vertical, tanθ = 1.8/(3*9.8) h = 4.9*3^2 = 44.1 m distance from base = 3*1.8 = 5.4 m
March 12, 2015

Math
there are initially 2 yellows out of a total of 10 marbles. chance of yellow on 1st draw: 2/10 with that yellow gone, there is now only 1 yellow out of 9 total, so the chance of a yellow on the 2nd draw is 1/9 So, the total probability is 2/10 * 1/9
March 12, 2015

chemistry
3g C = 1/4 mole 8g O2 = 1/2 mole So, you have CO2
March 12, 2015

factorise fully
Do you mean (p^2)(x) or p^(2x) 2q^y or 2q^2 y The mixture of exponents and multiplication seems unlikely. I will assume you meant p^2 x - 2q^2 y - 2 pqx + pqy = (p-2q)px + (p-2q)qy = (p-2q)(px+py)
March 12, 2015

maths
the area of the tank is 220m^2 So, you want to have a volume of 220*.21 = 46.2 m^3 15 km/hr = 4.167 m/s The area of the pipe is pi*.07^2 = 0.01539m^2 So, the water is flowing in at 4.167*0.01539 = 0.06414 m^3/s 46.2 m^3 / (.06414 m^3/s) = 720 s = 12 min = 0.2 hr
March 12, 2015

Integration
It occurs to me that a simpler way to go is x = sinθ, θ = arcsin(x) dx = cosθ dθ ∫x arcsin(x) dx = ∫ θ sinθ cosθ dθ = 1/2 ∫ θ sin2θ dθ Now use integration by parts to get u = θ, du = dθ dv = ...
March 12, 2015

Integration
now let x = sinθ dx = cosθ dθ ∫x^2 / 2√(1-x^2) dx = ∫ sin^2θ / 2cosθ * cosθ dθ = 1/2 ∫sin^2θ dθ = 1/4 ∫1-cos2θ dθ = 1/4 (θ - 1/2 sin 2θ) = 1/4 (θ - sinθ cosθ) = 1/4 (...
March 12, 2015

Integration
do these the same way, using integration by parts ∫x arcsin(x) dx Let arcsin x, du = 1/√(1-x^2) dx dv = x dx, v = 1/2 x^2 ∫ u dv = uv - ∫ v du ∫ x arcsin(x) dx = 1/2 x^2 arcsin(x) - ∫x^2 / 2√(1-x^2) dx Now you should be able to proceed.
March 12, 2015

Combining Like Terms
get rid of the parentheses, and you have -4-8-x-9x Surely now you can combine like terms, right?
March 12, 2015

Calculus 1
y = (√x)^3x lny = 3x ln√x = 3/2 x lnx 1/y y' = 3/2 (lnx + x/x) = 3/2 (lnx + 1) y' = 3/2 y (1+lnx) = 3/2 (√x)^3x (1+lnx) = 3/2 x^(3x/2) (1+lnx)
March 12, 2015

Calculus 1
y = x^(8cosx) lny = 8cosx lnx 1/y y' = 8(-sinx lnx + 8/x cosx) y' = 8 x^(8cosx) (8/x cosx - sinx lnx)
March 12, 2015

algebra
(10+8)/(10+8+42)
March 12, 2015

trig
the circumference of the frisbee is 12π in So, a point on the rim is traveling with a speed of 360*12π in/min Now just convert that to mi/hr
March 12, 2015

calculus
eh? did you not write down your calculations? How can you possibly not know how you arrived at an answer. I think you mean you are not sure whether your answer is right. At the moment in question, we have a 5-12-13 right triangle. x^2 + y^2 = 13^2 2x dx/dt + 2y dy/dt = 0 2(5)(...
March 12, 2015

math (answer check)
just make DE the hypotenuse, and consider horizontal and vertical legs. (-5,5),(9,5),(9,8) or (-5,5),(-5,8),(9,8) Trying to make DE one of the legs makes things a lot harder.
March 12, 2015

utd
The distance z is z^2 = (x-1)^2 + (y-1)^2 2z dz/dt = 2(x-1) dx/dt + 2(y-1) dy/dt At t=π/6, z=√((4(√3/2)-1)^2+(2(1/2)-1)^2) = 2√3-1 Note that at t=π/6, the point on the curve is (2√3,1) So, now we just have dx/dt = -4sint = -2 dy/dt = 2cost...
March 12, 2015

FACTORISE FULLY
a^3+b^3) = (a+b)(a^2-ab+b^2) so, (3x+y)^3 + (3x-y)^3 = ((3x+y)+(3x-y))((3x+y)^2-(3x+y)(3x-y)+(3x-y)^2) = (6x)(9x^2+6xy+y^2-9x^2+y^2+9x^2-6xy+y^2) = (6x)(9x^2+3y^2) = 18x(3x^2+y^2)
March 11, 2015

Pre-Calculus
You have his earnings as 100+5+10+15+... Since he gets $100 just for entering, all he needs to do is walk enough miles to get another $50 5+10+15+... is an arithmetic series of n terms, where Sn = n/2 (2*5+(n-1)5) >= 50 n >= 4 Check: 5+10+15+20 = 50
March 11, 2015

Vectors
Looks good to me.
March 11, 2015

Geometry
just find θ where sinθ = 25/32
March 11, 2015

Chemistry( HELP PLEASE, IM DESPERATE!!!)
These are all basically the same. For the first one, it takes 3 moles of O2 for every 2 moles of CH3OH. 13.97g CH3OH = 0.436 moles 5.45g O2 = 0.170 moles 3/2 * 0.436 > 0.170, so the O2 limits the reaction. Each 3 moles of O2 produces 2 moles of CO2, so we will get 2/3 * 0....
March 11, 2015

Calculus 1
f(x)=3 sin x+ln(5x) f'(x) = 3 cosx + 1/x Note that ln(5x) = ln5 + lnx So, the ln5 is just a constant, with zero derivative Of course, you could use the chain rule, so d/dx ln(5x) = (1/5x)*5 = 5/5x = 1/x
March 11, 2015

Math
(1+0.013)^n = 2 n = log2/log1.013 ...
March 11, 2015

Pre Algebra
zero
March 11, 2015

Calc
Use <= for less than or equal. a(t) = cos(t)-sin(t) v(t) = sin(t)+cos(t) + c v(0)=1, so c=0 v=0 when sin(t)+cos(t)=0. That is, sin(t) = -cos(t) sin(t)=cos(t) when t=π/4, so using that as a reference angle, that makes t = 3π/4 or 11π/4 Only 11π/4 is ...
March 11, 2015

Math
First, I doubt that 960t-5t is correct. If you meant v=960-5t, then clearly 960 is its maximum speed, whence it slowed down. If you meant v=960t-5t^2, that's a bit more interesting. Then the maximum speed is at t=96, and v(96) = 46080 But, if we stop counting at t=10, then...
March 11, 2015

Ap calc
a = 12t-6 v = 6t^2-6t+c v(0)=3, so c=3, and v = 6t^2-6t+3 s = 2t^3-3t^2+3t+c Since we assume zero distance at t=0, c=0. s(2) = 2*8 - 3*4 + 3*2 = 10
March 11, 2015

math
If the interior angle is x, then the sum of the other two interior angles is also x. Since they add up to 180, x=90. Also, since the sum of an interior angle and its adjacent exterior angle is a straight line, they sum to 180. So, the largest interior angle has the smallest ...
March 11, 2015

math
see the 1st related question below
March 11, 2015

Algebra
a = 49/10 b = 14/9 The reciprocal of b/a is a/b (49/10)/(14/9) = 49/10 * 9/14 = 441/140 = 63/20
March 11, 2015

math
4x + 5x = 90 x=10 The angles are 40 and 50 The smaller is increased by 10% from 40 to 44 So, the larger is decreased by 4 to 46. 4 is 8% of 50
March 11, 2015

math
If you meant that Logan is twice as old as Lindsay, then you are correct in setting it up as you did. Your solution, however, is bogus. x-5 + 2x-5 = 30 3x - 10 = 30 3x = 40 x = 40/3 No joy there. If it should have read Logan is 2 years older than Lindsay, then the equation is...
March 11, 2015

math
h/800 = sin 15°
March 11, 2015

physics
just see when the distances are equal: 120km/hr = 100/3 m/s, so 100/3 t = 2.5/2 t^2 t = 80/3 Now I expect you can handle the rest . . .
March 11, 2015

Algebra please explain
each year the boat is worth .85 as much as it was 92000*.85^10 = 18112.45 You are correct. I assume you were guessing between A and C, since the other two are clearly unreasonable.
March 11, 2015

important maths ques
As usual, draw a diagram. If you draw a line through the center, perpendicular to the chords, you cut them in half. The radius is the hypotenuse of two right triangles. One has a leg of 5, and the other has a leg of 12. So, 5^2 + 12^2 = r^2 12^2 + (17-x)^2 = r^2 5^2 + x^2 = 12...
March 11, 2015

maths please help and explain
2logx + 1 = log900 since 1 = log10, 2logx + log10 = log900 log x^2 + log10 = log900 log(10x^2) = log 900 10x^2 = 900 x^2 = 90 x = √90 3log(x-2) = 4.714 log(x-2)^3 = 4.714 (x-2)^3 = 51760.68 x-2 = 37.268 x = 39.268 16^(x-3) = 8^(2x+1) since 16 = 2^4 and 8 = 2^3, 2^(4(x-3...
March 11, 2015

MATHS
this is just like your last problem with the fruits. Try writing down in algebra what they told you. Come back if you get stuck, but show how far you got.
March 11, 2015

maths
What info did they give? d+p+a = 1134 .75d = a+252 p-96 = a+252 Now you can solve for the amounts.
March 11, 2015

Maths
Quite an interesting result, new to me. I see you have a typo. This problem is discussed here: http://math.stackexchange.com/questions/364002/prove-that-tan-1-fracyzxr-tan-1-fraczxyr-tan-1-fracxy
March 11, 2015

math
without trying to go into any existential discussion, let's just say that it is usually written as 1/4 I suspect there is more than that to your question . . .
March 11, 2015

math
or, if the slope is vertical, there's no derivative there. y = ∛x
March 11, 2015

math
not so. consider y = |x| Any time there's a cusp, or pointy place, on the graph, f is continuous, but since the slope changes instantly from one value to another, it is not differentiable there.
March 11, 2015

math
we all know that near x=0, sin(x) = x (or nearly) Since sin(pi-x) = sin(x), sin(pi-x) = pi-x
March 11, 2015

Trigonometry
just plug the numbers into the sum/difference formulas. Surely you can do that... Since both x and y are less than π/4 (why?), x+y is in QI. Since y > x, x-y is in QIV.
March 11, 2015

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