Friday
October 24, 2014

Posts by steve


Total # Posts: 26,075

Pre-Calculus
#1: I get -2/-7 = 2/7 #2: Nope. Parallel lines have the same slope. #3: slopes are -1/2 and 1 Neither
September 13, 2014

Math
C y" + (y')^2 + y^3 = f(x) is a 2nd order equation. You have to integrate twice to get y, and that introduces two constants. It is a 3rd-degree equation, because of y^3 Doesn't matter how many derivatives are present. Just their order. Better review DE's. Here...
September 13, 2014

science
of course. Not likely, though, imo.
September 13, 2014

still confused
well, you know the length is 2w-3, and you know w=25, so what's the trouble?
September 12, 2014

Algebra
AHA! My mistake. 24/6=4, not 6. Granted I was wrong, you should have caught my error and noted it, rather than just saying we disagreed.
September 12, 2014

Algebra
I showed my work. Why not show yours? Maybe we can come to some agreement...
September 12, 2014

Algebra
The result of each step is shown below: x 2x (2x)(3) = 6x 6x+24 x+6 6 The result is always 6
September 12, 2014

Physics
In x-y coordinates, A = (2.62,0) B = (0,2.26) C = (-1.4,0) D = (0,-2.8) A+B+C+D = (1.22,-0.54) That is 1.33 at E23.88°S
September 12, 2014

Math(Geometry) beware its hard for sixth graders!
Nice table, but you just need to understand the definition of the trig functions. In this case, h/19 = sin 42º h = 19*.6691 = 12.71 You should have immediately seen that your answer is wrong, because the ladder is only 19 feet long. How could it possibly reach 21 feet up ...
September 12, 2014

Math
the planes are approaching at 520+620=1140 mph By the time the 2nd plane takes off, the distance between the planes is only 1800-520=1280 miles At those speeds, they cover the distance in 1280/1140 = 1.123 hours I expect you can now answer the question.
September 12, 2014

Math
If $x at 4%, then .04x + .025(14000-x) = 458
September 12, 2014

math
If there are x with stripe only y with dot only z with stripe and dot, z = 6 (x+z) = 3y 3(y+z) = 2x So, x+y+z = 40
September 12, 2014

Algebra
minimum cost is at the vertex of the parabola, which occurs at x = 8/(2/5) = 20
September 12, 2014

Mathematica
or, convert to have the same denominator. 1/3 = 5/15 3/5 = 9/15 9 is 5+4, or 80% more than 5
September 12, 2014

Math
(a) recall that the vertex occurs at t = -b/2a = 20/32 = 5/8 So, figure h(5/8) (b) solve for t when h=0 (c) the point where he lands is a root of the function. h(t) = 0
September 12, 2014

Math
Looks like y = -|x^3| or y = -|x|^3 Not sure what the parent function would be. |x|^3 I guess, if all modifications to be considered are linear transformations.
September 12, 2014

Algebra
only if a=b
September 12, 2014

MATH
Base b only needs b symbols. After all b are used up, the next number is 10, and the bottom digit cycles through the other b-1 digits again, before going on to 20 (assuming b >= 2!)
September 12, 2014

algebra
T F (-2)^2 = 2^2 T
September 12, 2014

algebra
1 < 3x+2 < 12 subtract 2: -1 < 3x < 10 divide by 3: -1/3 < x < 10/3
September 12, 2014

Pre-Calculus/Trigonometry
Not A. It charges double for minutes over 250 Not B. flat rate up till x=250 Not C. Drops the $29 for x>250 Clearly D. Only charges the .35 for those minutes over 250.
September 12, 2014

Algebra
PI, not pie! v = pi r^2 h + 2/3 pi r^3 So, given the numbers above, pi (225) h + 2/3 pi (3375) = 10800 pi h = (10800pi - 2250 pi)/(225pi) = 38
September 12, 2014

maths
a=2 For details using elimination, see http://www.gregthatcher.com/Mathematics/GaussJordan.aspx
September 12, 2014

trigonometry - kindly help, needed badly
Draw a diagram, looking along the stream. If the width of the stream is w, and the height of the tree is h, then h/w = tan38°23' h/(w+200.6) = tan20°22' Eliminating w, we have h*cot38°23' = h*cot20°22' - 200.6 h = 200.6/(cot20°22' - ...
September 12, 2014

Math
Ahem 2 = Ab^-1 = A/b, so A = 2b 1 = Ab^3 = 2b^4 b = (1/2)^1/4 2 = A*2^(1/4) A = 2^(3/4) y = 2^(3/4) (1/2)^(x/4) or y = ∜(8/2^x)
September 12, 2014

Grade 9 Math
-(w^2 - 60w + 900) + 80w + 600 -w^2 + 60w - 900 + 80w + 600 -w^2 + 140w - 300
September 12, 2014

Algebra Grade 10
If we place the vertex at (0,2), then y = 2-ax^2 Since the span is 5 meters, the roots are at x = ±5/2 So, 2 - 25/4 a = 0 a = 8/25 y = 2 - 0.32x^2
September 12, 2014

Math Problem (please help)
How about 2(6*3)+2w = 36+2w
September 12, 2014

Math 112
I say see the related questions below and look at the response I posted yesterday.
September 12, 2014

Maths
consecutive angles are supplementary, so the angles are 44,136,44,136
September 12, 2014

Math
If 60% were boys, the ratio of boys:girls = 3:2 So, b/(b-1) = 3/2 2b = 3b-3 b = 3 So, 3 boys, 2 girls 60% boys
September 12, 2014

Algebra
(116 1/4) / (3 3/4) = 31
September 12, 2014

Math Problem (please help)
9x^3 - 30x^2 + 37x - 26 = 0 A little poking around with synthetic division show that f(x) = (x-2)(9x^2-12x+13) So, the only real root is x=2
September 12, 2014

Math Problem (please help)
Just solve -35x^3 + 2500x^2 - 275000 = 850000 using your favorite numeric method, or a graphing utility such as http://www.wolframalpha.com/input/?i=-35x^3+%2B+2500x^2+-+275000+%3D+850000
September 12, 2014

math
having no diagrams to consider, I'd say you did not explain anything well enough.
September 11, 2014

Math
any number between 0 and 2
September 11, 2014

Math
.00006 = 6*10^-5 I'd round up to 10^-4 789000 is almost a million, or 10^6 It is 7.89*10^5, so it rounds up to 1.0*10^6
September 11, 2014

algebra
anders-carmen = (anders-kaye) + (kaye-carmen) = 4.89 + 10 = 14.89 Rearranging things a bit, we are told Carmen finished 10 seconds before Kaye Kaye finished 4.89 seconds before Anders. alicia and donna are just noise.
September 11, 2014

math
h(t) = 51.6 - 4.9t^2 we want the time between when h(t) = 15.7 and h(t) = 1.90 So, just solve for t in 51.6-4.9t^2 = 15.7 51.6-4.9t^2 = 1.90 and subtract to find how long it will take to crush the man's skull.
September 11, 2014

college math
OK, v = 1/3 π r^2 h so, what? 3v = πr^2 h h = 3v / πr^2
September 11, 2014

college math
if x liters evaporate, the salt content remains the same, so .12(110) = .20(110-x) Now just solve for x.
September 11, 2014

college math
since distance = time*speed, 11x = 10(4.2-x) x = 2 So, the boat's speed is 2 knots. I expect now you can figure the distance.
September 11, 2014

Geometry
Nope. LM cannot be the midpoint of LM. If N is the midpoint of LM, then LN is half of LM, so 3x+5 = 2(5x+40) 3x+5 = 10x + 80 7x = -75 that makes the lengths negative. So, we must have M is the midpoint of LN. In that case, 5x+40 = 2(3x+5) 5x+40 = 6x + 10 x = 30 So, LM=MN=95 ...
September 11, 2014

math
#1: naturally, (1/4)/39.35 hours time = distance/speed
September 11, 2014

Magic Square
The sum of all the numbers is 99, so each row must sum to 33 10+11+12 = 33, so maybe that will form a diagonal. A little playing around, placing 19,20,21 in different rows and columns, gave me 19 3 11 2 10 21 12 20 1
September 11, 2014

math
p = r+4 6(r+4) + 8r = 38 So, solve for r and then figure p.
September 11, 2014

Differential Equations
Evidently you have not reviewed the definition of a linear DE: A differential equation is linear if the unknown function and its derivatives appear to the power 1 (products of the unknown function and its derivatives are not allowed) and nonlinear otherwise. So, the first ...
September 11, 2014

math
Hard to say. What is x supposed to represent? Any of the selections could be correct, depending on what x is.
September 11, 2014

Math
2=2
September 11, 2014

geometry
For x, -9 is 8 below -1 So, the other end is 8 below -9, or -17 Same for y. The other problem is the same method.
September 11, 2014

Math
Geez. We can, without loss of generality assume that a < b, so since the parabola opens upward, it dips below the x-axis between the roots. Naturally, it changes signs at a and b. UNLESS a=b In that case, there is a single root, and the polynomial does not change sign, as ...
September 11, 2014

Math
clearly the polynomial is zero if any of its factor is zero. So, one value of x is where x-a=0, os x=a I expect you can find the other.
September 11, 2014

Algebra 1
88-7.5 <= x <= 88+7.5
September 11, 2014

math
19:7 > 7:26
September 11, 2014

math
what "result" must be 6 digits? x+y+z = 39 y = z/2 x = z-1 x=15 y=8 z=16
September 11, 2014

Calculus II
Looks good to me. I'd have just written 9/√51, but some folks get itchy over radicals in the denominator.
September 11, 2014

math
the planes are approaching at 520+620=1140 mph By the time the 2nd plane takes off, the distance between the planes is only 1800-520=1280 miles At those speeds, they cover the distance in 1280/1140 = 1.123 hours I expect you can now answer the question.
September 11, 2014

math
since time = distance/speed, d/4 + d/2 = 126 Now just solve for d
September 11, 2014

math
If $x at 4%, then .04x + .025(14000-x) = 458
September 11, 2014

math
The new machine completes 2/13 of the job. So, the older machine requires (11/13)/(1/15) = 12.7 hours to do the rest.
September 11, 2014

math
Hmmm. I may have been hasty. Anyway, if there are x oz. of $3.50 alloy, the rest (30-x) is the $7.00 alloy. So, check to be sure that the value of silver adds up: 3.50x + 7.00(30-x) = 6.30(30) x = 6
September 11, 2014

math
we've done a lot of these mixture problems for you. Why not try some yourself, and we can check your work...
September 11, 2014

Math
Do you not see that you are missing some data here?
September 11, 2014

math
Tell you what. I'll solve one, and you can try the others. Post your work if you get stuck. x^2-3(2x+3)=0 x^2-6x-9 = 0 x = (6±√(36+36))/2 = (6±6√2)/2 = 3±3√2
September 11, 2014

Grade 10 Maths
recall that the vertex of a parabola is at x = -b/2a In this problem, that is x = -20/-1 = 20
September 11, 2014

1
First, find the speed of sound, and then recall that distance = time * speed. Then, since time = distance/speed, divide that distance by the speed of light.
September 11, 2014

Year 10 Alegbra
A = 8w - 2w^2 As you recall, the vertex of a parabola (in this case, the maximum area) is achieved at x = -b/2a In this case, that's x = -8/-4 = 2 Or, you can note that the roots of A=0 are 0 and 4. The vertex is midway between the roots, at x=2.
September 11, 2014

Year 10 Alegbra
depends on what the question is, no?
September 11, 2014

math
so, you gonna share those roots with us?
September 11, 2014

Math: pre calculus
If the width of the pens is x, and the overall length is y, then 3x+y = 240 The area is a = xy = x(240-3x) = 240x - 3x^2 This is just a parabola, with vertex at x = 40 So, the pens are each 40 by 60 ft. As usual, maximum area is achieved when the available fence is divided ...
September 11, 2014

mathematics
just as x^a * x^b = x^(a+b) log(a*b) = log(a) + log(b)
September 11, 2014

MATH
ummm, 53x5 = 265
September 11, 2014

Force of Gravity
since F = GMm/r^2 when r doubles you have GMm/(2r)^2 = Gmm/4r^2 = GMm/r^2 * 1/4 = F/4
September 11, 2014

Geometry
we have if p then q we are told p is true, so therefore, q: the measure is 90 degrees.
September 11, 2014

8th Grade math
False who says they have to be spaced 1 degree apart? If they are spaced 1 minute apart, there are 60*360 = 21,600 rays
September 11, 2014

Quantitative Reasoning (math)
360/60 = 6
September 11, 2014

8th grade math
Nope.
September 11, 2014

8th grade math
False. Between any two points there is another. Following that reasoning, between any two points there are infinitely many others.
September 11, 2014

Math
The 10x10 cake is 5x5 pieces, so it takes 4+4=8 cuts to do the job. That is 5 seconds per cut. The 12x12 cake is 6x6 pieces, so it will take 5+5=10 cuts, or 50 seconds. Assuming a 12" cut can be made in the same time as a 10" cut!
September 10, 2014

Math
If the original selling price was s, then she paid 3*s(1-.20)+10
September 10, 2014

Math
If there were originally b boys out of s students in the class, b/s = 2/3 b/(s+2) = 3/5 Or, b = 2s/3 5b = 3s+6 So, 5(2s/3) = 3s+6 10s = 9s+18 s = 18 Now you should be able to answer the question.
September 10, 2014

pre calculus
You know that a parabola with vertex at (h,k) is y = a(x-h)+k So, we now have y = a(x+3) - 10 Now just plug in (2,-5) to find a.
September 10, 2014

Geometry
Now you know that RSP = PST = -17 So, since RST = RSP + PST, RST = -34 Not sure what the negative values indicate. Sure there's not a typo in the problem?
September 10, 2014

Geometry
Use your distance formula: AB = √((2-0)^2+(7-3)^2) = √(4+16) = √20 = 2√5
September 10, 2014

math
Actually, the volume of a cone is v = 1/3 π r^2 h
September 10, 2014

math
2(w + 2w-3) = 144
September 10, 2014

Math
1,2,3,4,5,6,7,8,9,10,11,12,13 add up to 91. So, it looks like we have 1,2,3,4,5,6,7,8,9,10,11,12,14
September 10, 2014

math
Not quite sure what you're doing there. If a side of the square is 45, its perimeter is 180. Thus, the perimeter of the triangle is 90. So, each side of the triangle must be 30.
September 10, 2014

algebra 1
If x >= 0, |x| = x If x < 0, |x| = -x So, from what we have above, x >= 0 x-2 < 0, or x < 2 So, 0 <= x < 2
September 10, 2014

Trig
If the nearer observer is at distance x from the obelisk, then we have h/x = tan 65° h/(x+25) = tan 44° so, eliminating x, just solve for h in h/tan65° = h/tan44° - 25 h = 25/(cot44°-cot65°)
September 10, 2014

math
400m / 92s = 4.35 m/s or, 400m / 1.533 min = 260.9 m/min
September 10, 2014

college algebra
If x oz. of 1% are used, then the rest (3-x) are 5%, so .01x + .05(3-x) = .04(3) x = 3/4 So, 3/4 oz of 1% and 9/4 oz of 5% Note that 4% is 3/4 of the way from 1% to 5%, so 3/4 of the total is the 5% strength.
September 10, 2014

college algebra
If x is at 8%, the remainder (22000-x) is at 6% so, .08x + .06(22000-x) = 1680 ...
September 10, 2014

math
just plug in your numbers: h(t) = -16t^2 + 84t + 60 assuming he kicks it straight up. Now just plug in t=2
September 10, 2014

Math
Since A+B+C=180, C=94.24 So, using the law of sines, c/sinC = a/sinA Now just plug and chug.
September 10, 2014

Algebra!!!! HELP
Since F=kx, F/x is constant. So, (a) 120/x = 265/0.15 (b) F/0.3 = 265/0.15 Note that you can answer these questions without even determining the value of k explicitly.
September 10, 2014

math
Just use the quadratic formula: x = (-(c-a)±√((c-a)^2 - 4(b-c)(a-b)))/(2(b-c)) You can play around with that some, but I don't see much in the way of simplification. http://www.wolframalpha.com/input/?i=%28b-c%29x%C2%B2+%2B+%28c-a%29x+%2B+%28a-b%29
September 10, 2014

math
(6x+2)/4 + (2x²-1)/(2x²+2) = (10x-1)/4x Clear fractions by using the common denominator of 4x(x²+1). This requires that x≠0. (6x+2)(x(x²+1)) + (2x²-1)(2x) = (10x-1)(x²+1) (6x^4+2x^3+6x^2+2x) + (4x^3-2x) = (10x^3-x^2+10x-1) 6x^4 - 4x^3 + 7x^2...
September 10, 2014

calc
If you found T(t) = r'/|r'|, then you should be able to get N(t) = T'/|T'| Where do you get stuck?
September 10, 2014

math
(1) 2(x + x-3) = x(x-3) x = 1 or 6 But x=1 isn't viable, so only x=6 (2) 2(x+x) = x^2 x = 4
September 10, 2014

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