Wednesday
August 27, 2014

Posts by Steve


Total # Posts: 24,450

Hard Geometry Problem
a negative scale factor changes size, and reflects through the dilation center. If it were positive, the whole reduced triangle would of course remain within ABC. But, by flipping through G as well as scaling, some of A'B'C' will lie outside of ABC.
August 1, 2014

algebra
c = p+37 i = 2p-38 c+p+i = 447 Now just solve for c,p,i using your favorite method.
August 1, 2014

mat/117
since the discriminant is negative, there are no real solutions.
August 1, 2014

mat/117
just start substituting for n: a1 = 2*1 = 2 a2 = 2*2 = 4 ...
August 1, 2014

math
what do we know? c = 2/3 p r = 1/2 c t = 100 = r-90 So, what is p? p = 3/2 c = 3/2 (2r) = 3r = 3(t+90) = 3(190) = 570
August 1, 2014

math
well, how many cubic yards in a single post? Expressing the dimensions in yards, the volume is (9/36)(9/36)(6/3) yd^3
August 1, 2014

math
Clearly that would be (5.75+8.2)-(6.2+9.4)
August 1, 2014

math
That would total up to 0.75 + 0.50 + 0.45 km
August 1, 2014

Logarithms
If the fraction is a/b c then you'd have +logc If, as I suspect, it is a/(bc) then it is indeed loga - (logb+logc) = loga - logb - logc
August 1, 2014

Chemestry
just look up element #50 on the periodic table. Protons determine the atomic number. It's short two electrons, so the charge will be +2.
August 1, 2014

first chemistry
just look up the formula for aspirin (acetylsalicylic acid) and add up the weights of all the atoms involved.
August 1, 2014

chem
Since the required amounts of the two reagents have almost the same mass, H2S will be the limiting one, since twice as many moles of that are required. So, it will be the limiting reagent. So, figure how many moles of H2S are in 87.1g, and calculate the mass of 3/16 that many ...
August 1, 2014

Geometry
Since the vertices are 36° apart, and X and R are 4 positions apart, it is indeed a central rotation of 144°. However, we want to rotate about U, not the center of the decagon. If you draw the figure, and if we call the center of the decagon A, then you can see that &...
July 31, 2014

physics
The horizontal speed does not change. It remains at 7.5 cos51° = 4.72 m/s The vertical speed is given by v = Vo -9.8t, so it ends up at 7.5 sin51° - 9.8*1.5 = -8.87 m/s So, the final speed is √(4.72^2 + 8.87^2) = 10.05 m/s
July 31, 2014

Math
use the two-point form of a line and you can see that (y-5)/(x+1) = (5+1)/(-1-2) y-5 = -2(x+1) y = -2(x+1)+5 So, y(x+1) = -2((x+1)+1)+5 = -2(x+2)+5 = -2x-4+5 = -2x+1
July 31, 2014

Maths
I'd say that would be 8*6 = 48
July 31, 2014

Calculus
Using the comparison test, the series diverges.
July 31, 2014

AP Calc
let the center of the cable be at (0,220). That becomes the vertex of the parabola, so the equation is y = ax^2+220 Since y(2100) = 750, that means that a*2100^2 + 220 = 750 a = 530/2100^2 = 0.00012 So, we now know that the height y = 0.00012x^2 + 220 Now, we know y' = 0....
July 31, 2014

Translations
what do you mean by "that's not right?" What calculation did you do? Without loss of generality, we can take the distances to be measured along the x-axis. We have two points, P and Q on the x-axis, where OQ = 4(OP) because of the dilation. Since PQ=18, that ...
July 31, 2014

Translations
all distances also scale by a factor of 4.
July 31, 2014

Physics
The trains approach at 260km/hr The distance to cover is 285km. So, it takes 285/260 hrs to meet. In that time, the train from Calgary covers 285/260 * 140 = 153 km
July 31, 2014

geometry help!! answer all questions!! please
Posting a whole homework assignment with no evidence of any attempt on your part will get you scant help here. Surely you have covered the relevant material, so you must have some ideas on at least some of the problems... The hints I posted earlier should get you started on ...
July 31, 2014

Geometry
P(x,y) -> P'(x+3,y-3) reflection over y=x is (x,y) -> (y,x) reflection over the y-axis is (x,y) -> (-x,y) reflection over the x-axis is (x,y) -> (x,-y) and so on. Where do you get stuck?
July 31, 2014

Math
distance is just the integral of velocity. So, just integrate, and evaluate at the ends of the interval.
July 31, 2014

Math
y = -(x-1)(x-4) so you want to integrate between the roots, in the interval [1,4] a = ∫[1,4] -x^2+5x-4 dx = -1/3 x^3 + 5/2 x^2 - 4x [1,4] Now just evaluate at the ends and subtract.
July 31, 2014

trigonometry
The problem states: Find the formula of the trigonometric function that models the height H of the weight t seconds after it reached its maximum height. Your function is supposed to model the height starting when it is at its maximum. So, let that be t=0.
July 31, 2014

prealgebra
you know that for such a triangle, the sides are in the ratio 1:√3:2 So, the short side is 41 The long side is 41√3 The hypotenuse is 41*2 The functions of 30° are standard values, which it would be well to learn.
July 31, 2014

math
All you want is the number of permutations for 3 out of 4: 4P3 = 4*3*2 = 24 You can pick the first in 4 ways. Now there are 3 choices for the 2nd, and 2 left for the 3rd.
July 31, 2014

math(precalculus)
You don't need any c. It can be absorbed into a and b. Actually, you have solved the problem. Pick any value for c, and plug it in. As long as a=c and b=-4c, R(x) will work. So, make things easy. Let c=1. As I worked it out, R(x) = ???/(x+1)(x-2) Since y=0 is the asymptote...
July 31, 2014

Math
heads: r+c = 35 feet: 4r+2c = 94 Now just solve for r and c, in any of several ways.
July 31, 2014

Science/Physics
weight (force) = mg Look up g if you don't know it. Now, divide that by the relative gravity of the moon. For example, if the moon has 1/2 the gravity of earth, you will need double the mass for the same weight.
July 31, 2014

Physics
The resultant velocity is v = (106,106) + (0,20) = (106,126) |v| = 164.7 The angle x obeys tan(x) = 126/106 The time taken is 500,000/164.7 seconds
July 31, 2014

Math
surely you can see that A=3 B=pi/20 C=0 D=7 I mean, just read it off. Now employ your skills to convert your cos(x) to sin(pi/2-x) A and D stay the same.
July 30, 2014

Math
since y is a max when t=0, we want a cosine function, since cos(0) = 1. y = 7+3cos(pi/20 t) because the period is 40 seconds, and the level varies between 7+3 and 7-3 feet.. C=0 because cosine is a max at t=0, so there is no offset. Naturally, you can now write the sine ...
July 30, 2014

Alegbra1
depends. How much of all that is under the radical sign? Once you specify that, just remember that the domain of √u is u>=0.
July 30, 2014

Math
20% + 15% = 35% given away. That leaves 65%, so .65x = 520 Now just solve for x.
July 30, 2014

math - huh?
I see several problems. who the heck is Mary? Is Mary really male?
July 30, 2014

math
f+l = 80 2/3 f = l-10 so, 2/3(80-l) = l - 10 160-2l = 3l-30 190 = 5l l = 38 check: initially there were 38 local and 42 foreign after removing 10 local and 14 foreign, there were 28 of each.
July 30, 2014

PreCalculus
just make the usual substitution. y = rsinθ x = rcosθ so, that means r^2sin^2θ/25 - r^2cos^2θ/9 = 1 r^2(9sin^2θ-25cos^2θ) = 225 r^2 = 225/(9sin^2θ-25cos^2θ) see the expected vertical hyperbola at http://www.wolframalpha.com/input/?i=plot...
July 30, 2014

statistics
Since there are 10 choices, I'd just use the nth digit of 3 numbers chosen from the random number table. which n depends on how many digits in each entry; just make sure all use the same n. Or maybe add up the digits and take the last digit of the sum.
July 30, 2014

Maths
1+2+4=7, so if we divide the sum into 7 equal parts of size x, 7x = 126 x = 18 So, the shares are 18,36,72
July 30, 2014

Math
find the distance between the two points, as usual. Now, since the area of a square is a = d^2/2, just figure that.
July 30, 2014

math
clearly, if the angle is x, tan(x) = 7.15/10.1
July 30, 2014

Math - grrr.
all that anti-derivative stuff is too much for me that early. Thanks for the fix. I'm sure Tim caught the error and fixed it though. . . . Right, buddy?
July 29, 2014

Math
since y" = 6x y' = 6x+a y = 3x^2+ax+b we know the slope is y'(1) = -3, so 6(1) + a = -3 a = -9 so, y = 3x^2-9x+b since 5-3x=2 at x=1, y(1) = 2, and we have 3-9+b = 2 b = 8 and y = 3x^2-9x+8 See the graphs at http://www.wolframalpha.com/input/?i=plot+y%3D3x^2-9x%...
July 29, 2014

PreCalculus
sin(x)sec(x) - 2sin(x) = 0 sin(x)(sec(x)-2) = 0 sin(x) = 0 sec(x) = 2 Those are pretty standard angles, so listing the solutions should be easy.
July 29, 2014

geometry
The diagonals cross in the center, so the acute angle is the vertex of an isosceles triangle with height=24 base=14 so the acute angle x obeys tan(x/2) = 7/24
July 29, 2014

Geometry
If the dimensions are x,y,z then we have 2xy+2xz+2yz = 22 4x+4y+4z = 24 xy+xz+yz = 11 x+y+z = 6 How about 1,2,3 diagonal is √14
July 29, 2014

mathematics
70%
July 29, 2014

algebra
I'd do it by taking the log of the values, and using a normal linear best-fit on the log values. Where log(15500/v) = log4, that's the number of years you want.
July 29, 2014

math
4 = 2^2 4/(2^x) = (2^2)/(2^x) = 2^(2-x) Now, just solve the equation. Hint: 2^(x-2) = 2^x / 4
July 29, 2014

Trigonometry
The individual displacements are 150 @ 220° = (-96.4,-114.9) 130 @ 130° = (99.6,-83.6) So, the final location is at (3.2,-198.5) Just find the distance from there to the origin.
July 29, 2014

math
On the other hand, if you meant 27√3, that makes b=7/2
July 29, 2014

Finite Math
clearly it's 500-x
July 29, 2014

Math
just start by listing the facts: width=w length=w+6 height=2 area is the 4 sides + bottom = 2(width*height)+2(length*height)+(length*width) = 2(2w)+2(2(w+6))+w(w+6) = 4w + 4w+24 + w^2+6w = w^2 + 14w + 24 So, now we know that w^2+14w+24 = 280 w^2+14w-256 = 0 Solve that for w, ...
July 28, 2014

math
after 1/8 were purchased, 7/8 were left. So, now we have 7/8 x + 10 = 52 7/8 x = 42 x = 48
July 28, 2014

math
a/p = 3/5 (2/5 a)/(p-40) = 2/5 a=60 p=100 so, she paid 60(.30)+100(.45) = $63.00
July 28, 2014

math
3278164781246
July 28, 2014

math
9/180 = 0.05 = 5%
July 28, 2014

chemistry
32 days is 4 half-lives. So, the mass is reduced to 1/2^4 = 1/16 of 40mg, or 2.5mg
July 28, 2014

Math
so far so good. Now just solve for b and plug that into your formula. Then check that (-3,-8) satisfies the equation.
July 28, 2014

Math
plot the point. Since the slope is 2/3, go right 3 and up 2 and plot another point. Draw the line connecting the two points.
July 28, 2014

physics
the difference is 4.9µC. So, move half that, or 2.45µC. Now just convert that to no. electrons.
July 28, 2014

math/help
4 1/6 = 25/6 1 1/6 = 7/6 so, (25/6)/(7/6) = 25/7 3 3/1 ??? fix that and work it as in the above one.
July 28, 2014

math
just as usual. Where is y" positive? e^-3t is always positive, so all you need is 2t-3 > 0 t > 3/2 e^3/2 = 4.48, and you can see from the graph that it is concave upward for x > 4.48 http://www.wolframalpha.com/input/?i=plot+x+%3D+e^t%2C+y+%3D+te^-t+for+1%3C%3Dt%...
July 28, 2014

math
x = e^t y = te^-t dy/dx = y'/x' = (1-t)e^-t/e^t = (1-t)e^-2t d^2/dx^2 = (x'y"-x"y')/x'^3 = ((e^t)(t-2)e^-t - (e^t)(1-t)e^-t)/e^3t = (2t-3)e^-3t or, do it directly x = e^t, so y = lnx/x y' = (1-lnx)/x^2 = (1-t)e^-2t y" = (2lnx-3)/x^3 = (2t...
July 28, 2014

Science
why do you include a third dimension? The taxi cannot travel vertically. The total displacements are 20+6=26 blocks south 15 blocks east. So, √(15^2+26^2) = √901 = 30.0
July 28, 2014

physics
15.7 + 17.5
July 28, 2014

math
1/2 * 1/2 * 1/6
July 28, 2014

Algebra
Start by expanding the parentheses: 3(x-1) -2(x^2+3x+4)-5(x+9) 3x - 3 - 2x^2 - 6x - 8 - 5x - 45 Then collect terms of like degree: -2x^2 + (3-6-5)x + (-3-8-45) -2x^2 - 8x - 56
July 27, 2014

Math
If their heights are k and r, then k/375 = sin 32° r/375 = sin 38° So, the difference is r-k = 375(sin38°-sin32°)
July 27, 2014

math
that's because you mixed up dollars and cents. It asked for only dollars.
July 27, 2014

math
3:40 to 6:20 is just 2 hours and 40 minutes. That should get you going.
July 27, 2014

Math
Assuming you mean "I" and not "O", just pick any two values for x and calculate the y: x=0: y=4 x=4: y=5 So, the points (0,4) and (4,5) are on the line. Plot them, and draw a line between the two points.
July 27, 2014

math
There are only 3 colors. Any group of more than 3 cards will have to have a duplicate color.
July 27, 2014

Statistics
0.066-0.033 < p < 0.066+0.033
July 27, 2014

english
That "ing" is a big clue for a gerund.
July 27, 2014

chemistry
when you say it was immersed, that implies there was some other liquid in the cylinder. If all you mean is that the sodium exactly filled the cylinder, then the density is obviously 405.5g/32.5ml = 405.5/32.5 g/ml
July 27, 2014

Chemisrt
What you have is just D = D0*x where x is all that exponential stuff. So, D0 = D/x Of course, R is not specified. If it's R you are looking for, then just work it out like this: exp[-Ea/R*T] = D/D0 -Ea/R*T = ln(D/D0) R = -Ea*T/ln(D/D0)
July 27, 2014

maths
if you mark off a length of 4, you can easily construct a length of 30. Double the 4 to 8, double the 8 to 16, double the 16 to 32. Halve the 4 to get 2, and subtract that from the 32. Now construct the leg BC, and the right angle at C. Then mark off a circle of radius 30 to ...
July 27, 2014

algebra
take a look at http://www.jiskha.com/display.cgi?id=1406381756
July 27, 2014

math
just plug in the values and see. For example, take (1,-2). Is 3*1 + 3*1 - 6 < -2 ? 0 < -2 ? No. Now try the others.
July 27, 2014

math
if you can recognize a quadratic and an inequality (as opposed to an equation), you should have no trouble picking the correct choice.
July 27, 2014

math
2(w+1.2w) = 88 4.4w = 88 w = 20 so, area = 20(1.2*20) = 480
July 27, 2014

calculus 2
dy/dx = y'/x' = (-3sint)/(2cost) = -3/2 tan t d^2y/dx^2 = (x'y"-x"y')/x'^3 = ((2cost)(-3cost) - (-2sint)(-3sint))/(8cos^3 t) = -3/4 sec^3 t Check: y = 3/2 √(4-x^2) y' = -3/2 x/√(4-x^2) y" = -6/(4-x^2)3/2 I'll leave it to ...
July 26, 2014

calculus 2
I think she means y = ∛x
July 26, 2014

Math
Correct. So, 5/11 - 7/11 = -2/11
July 26, 2014

Math
you're working with 11ths. So, what's 5-7?
July 26, 2014

math
s = ∫[0,6π] √((dx/dt)^2 + (dy/dt)^2) dt = ∫[0,6π] √((1-2cost)^2 + (2sint)^2) dt = ∫[0,6π] √(1-4cost+4cos^2t + 4sin^2t) dt = ∫[0,6π] √(5-4cost) dt
July 26, 2014

trigonometry
15rev/12sec = 5/4 rev/sec = 5π/2 rad/s That's the speed of the smaller pulley Assuming they are both attached to the same belt, the larger pulley's rotational speed is 6/20 the speed of the smaller one.
July 26, 2014

Math - trig
no, no. It's just a quadratic equation, in cosx, rather than just x using the quadratic formula, we have cosx = (1±√3)/4 or, -0.183, 0.683 So, just find the angles with those values as cosine.
July 26, 2014

math
the price, for n >= 150, is p(n) = 200-n Revenue is price*quantity, so r(n) = n(200-n) = 200n-n^2 That's just a parabola. The vertex is the point of maximum revenue. That's just algebra I, so no sweat. . . . right?
July 26, 2014

math
Looks like (a) to me. Just use the quadratic formula.
July 26, 2014

trig
draw a right triangle with the tops of the poles as the ends of the hypotenuse, and the bottom side perpendicular to the poles. You have a 5-12-13 triangle. It is useful to learn some of the basic triangles with integer sides -- they pop up frequently. 3-4-5 5-12-13 8-15-17 7-...
July 26, 2014

College Algebra
All you need is f(-1)*g(-1) = 4 f(x) = 2 g(x) = 2 will work, but they are rather trivial. I'm sure you can come up with two functions that work.
July 25, 2014

Algebra
Clearly E cannot exceed 5, since even with borrowing, A cannot exceed 10. That would mean something like FL50 -B55 ------- MO95
July 25, 2014

Algebra
1/3 of the mice are female, so 1/6 of the mice are white female 1/6 of the mice are brown female 3/5 are brown, so 3/5-1/6 = 13/30 are white male 1-(1/3+13/30) = 7/30 are brown male So, brownmale/whitemale = 7/13
July 25, 2014

MATH WORD PROBLEMS
to be centered, the extra space must be divided into two equal parts.
July 25, 2014

College Algebra
q(x) = 73(x+1)^2+2 h(x) = x^2 g(x) = (x-1)(x-2)(x-3) Since x^0=1 for any x, we have s(x) = 2*a^(kx) for some a and k. 2*1/2 = 1, so s(x) = 2*4^(-x/2) r(x) will involve something/(x-3) x-2 is zero at x=2, so r(x) = (x-2)/(x-3) will work
July 25, 2014

College Algebra
reflected: -|x| stretch vertically: -4|x| shifted: -4|x+3| see http://www.wolframalpha.com/input/?i=plot+y%3D|x|%2C+y%3D-4|x%2B3| You want t where 1(1+.075/4)^(4t) = 7200 The rule of 72 indicates it should double about every 10 years. Since 7200 is about 2^13, I expect it will...
July 25, 2014

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