Wednesday
October 1, 2014

Posts by steve


Total # Posts: 25,381

math
recall that ∫ du/(a^2+u^2) = 1/a arctan(u/a) now note that x^2+4x+13 = (x+2)^2 + 3^2 Nuff said? I get π/12
August 23, 2014

equations
1.25x = 3.5 - 0.4x 1.65x = 3.5 ok?
August 23, 2014

maths
Draw a diagram. If you draw a horizontal line from the top of the 6m pole to where in intersects the 11m pole, then you have a right triangle with legs 5 and 12. You should be able to recognize the ubiquitous 5-12-13 triangle. The tops are 13m apart.
August 23, 2014

calc
As usual, just use the chain rule: Let u = e^3x, and you have d/dx arctan(u) = 1/(1+u^2) * du/dx = 1/(1+u^2) (3e^3x) = 3e^3x/(1+e^6x)
August 22, 2014

Algebra
correct answer, but when typing online where there is no vertical fraction formatting, it's better to use 8/(x-m) That way it will not be confused with 8/x - m Normally, when evaluating expressions, multiplication is done before subtraction, unless parentheses indicate ...
August 22, 2014

Algebra
actually, you already have the difference. What you have done is find the quotient and then simplified it.
August 22, 2014

college algebra
If there are x kg of Brazilian coffee, then the rest (420-x) is Turkish. So, 10x + 13(420-x) = 12*420 x = 140 Note that 140 is 1/3 of 420, meaning that it drags the price down 1/3 of the way from 13 to 10, or $12.
August 22, 2014

math
you want to convert 100 pages to minutes. Your conversion factor is 20 minutes = n pg 20min/n pg = 1 Now multiply vy that to cancel the unwanted units: 100 pg * 20min/n pg = 2000/n min
August 22, 2014

math
Better take a look at http://mathmistakes.info/facts/CalculusFacts/learn/doi/doif.html So, what you have is √(1+(2x)^2)(2) = 2√(1+4x^2) at x=√2, that is 2√(1+8) = 2*3 = 6
August 22, 2014

Algebra
y = 3/(2x) so we want the minimum of 10x + 3/5 * 3/(2x) = 10x + 9/(10x) take the derivative and you have 10 - 9/(10x^2) set that to zero and you get 100x^2 - 9 = 0 (10x-3)(10x+3) = 0 x = ±3/10 So, at x = 3/10, y = 5 and 10x+3y/5 = 3+3 = 6
August 22, 2014

math
g'(1/2) = 4(1/2)(2-1/4) = 2(7/4) = 7/2 So, g is increasing at x = 1/2 Have you looked at the graph? http://www.wolframalpha.com/input/?i=4x^2+-+3x^4 Clearly only (b) is true
August 22, 2014

math
g' = 8x-12x^3 = 4x(2-x^2) g" = 8-36x^2 g' changes sign in x<1, so not (a) g'=0 and g"≠0 at x=0, so (b) g" changes sign, so not (c) so, (b) is the only true statement
August 22, 2014

math
you are correct
August 22, 2014

math
exactly 75%=3/4 implies the number is a multiple of 4, so the candidates are 40,44,48 exactly 1/6 implies it is also a multiple of 6, so 48 students
August 22, 2014

Math
9 clearly cannot be on a corner, so we have X9X X7X XXX Now, the only choices along the top are 1,2, so we have 192 X7X XXX 8 cannot be on a corner, because then we'd need 2,2 or 1,3 twice. It must be on one of the sides: 192 87X 3XX Now, 3+9=12 and 2+10=12 We still need ...
August 22, 2014

Algebra
(x-1)/(x-3) = √(17-x) (x-1)^2/(x-3)^2 = (17-x) x^2-2x+1 = -x^3+23x^2-111x+153 x^3-22x^2+109x-152 = 0 No rational roots here, so you will need to resort to a graphical or numeric method to get the desired accuracy. http://www.wolframalpha.com/input/?i=x^3-22x^2%2B109x-152
August 22, 2014

math
If the first basket has x and the second has y, x = 4/3 y x = y+3 x = 4/3 (x-3) x = 4/3 x - 4 1/3 x = 4 x = 12
August 22, 2014

algebra
P e^(.0855*(8+125/365)) = 225500 P = 110502.63
August 22, 2014

algebra
Assuming you want to factor it, grouping is probably the easiest way: 4ax+8a-10x-20 2(2ax+4a -5x-10) 2(2a(x+2)-5(x+2)) 2(2a-5)(x+2)
August 21, 2014

Algebra
sure. You can have any positive number of rows or columns.
August 21, 2014

Math
2 2/5 % = 12/5 % = (12/5)/100 = 12/500 = 3/125
August 21, 2014

math
(3/4 mi)/(9/8 mi/hr) = 3/4 * 8/9 hr = 24/36 hr = 2/3 * 60 min = 40 min
August 21, 2014

Geomentry
assuming RST are collinear, RT = RS+ST, so 8y+4 + 2x-2 = 64 2x = 64-8y-4+2 2x = 62-8y x = 31-4y Assuming the y is a typo, 8x+4 + 2x-2 = 64 10x = 62 x = 6.2
August 21, 2014

math
6/4
August 21, 2014

Math
Get the w stuff all alone G-4x-4/3 = 1/2 w Now multiply by 2 and you have 2(G-4x-4/3) = w
August 21, 2014

math
Because you have added 0 hudredths. Adding 0 of anything leaves the result unchanged. 10.6 = 10.60 = 10.6000000000000000000
August 21, 2014

Math
In that case, there is no way to tell. You must know how many rows, and how many seats in each row. And who cares which day it was?
August 21, 2014

math
Looks like $1.25 for the first 1.5 miles, and $.45 more for every 1/2 mile beyond that. So, since 2 5/8 = 1 1/2 + 1/2 + 1/2 + 1/8, the charge is $1.25 + 0.45 + 0.45 + 0.45 = $2.60 Now work on the other parts.
August 21, 2014

math
we know that (2x+12)^2 + x^2 = (2x+18)^2 expand all that and solve the quadratic, and you get x = 30 check: 30^2 + 72^2 = 78^2 That's just 6 times a 5-12-13 triangle
August 21, 2014

math
x^2-2x+1 - 4 x^2-2x-3
August 21, 2014

Algebra
correct!
August 21, 2014

physics
In terms of x & y, 186@E23°N = 171.21,72.68 327@N43°W = -223.01,239.15 Add them up: -51.80,311.83 That is 361.10 at 99.43° or, as a heading, 361.10@N9.43°W
August 21, 2014

MAth
Nope. Treat || like parentheses for grouping. Then, when everything inside has been evaluated, apply the absolute value: |13|-7x|-2+8|/6 13-7x|6|/6 13-7x6/6 13-7x1 6
August 21, 2014

physics
The swimmer's direction should be the hypotenuse of the diagram. Then, the current makes the resultant velocity perpendicular to the bank. The angle is thus upstream at an angle of arccos(1.5/3.76)=66.5° relative to the bank. That makes the speed relative to the shore...
August 21, 2014

math
For m minutes, A: 25.00+0.10(m-30) B: 20.00+0.12(m-30) So, just solve for m when A=B The language used for this problem is rather odd. Not at all what I'd expect from a school text.
August 21, 2014

math
since 7y=28x, y = 4x 6x+4(4x) = 40 22x = 40 x = 20/11 x^2 = 400/121
August 20, 2014

Math
just subtract his initial loss from the subsequent profit: 1580-415 = ?
August 20, 2014

Algebra
sounds good. You might also note that for an exponential function y = f(x), log(y) is linear.
August 20, 2014

Geometry - eh?
Hard to say. Just noting the degrees separating the hands tells nothing about the actual time. And, since you don't specify which hand is at 70 degrees, that's no help either. Want to rethink the question?
August 20, 2014

Math
If you mean (225-256)^2 that's just (-31)^2 = 961 If you mean 225-256^2 that's -65311
August 20, 2014

Algebra
easy. Note that y^3 / y^10 = y^3 / y^3*y^7 The y^3 factors cancel, and you are left with 1/y^7 Or, use the rule that in division, you subtract exponents, so y^3/y^10 = y^(3-10) = y^-7 = 1/y^7
August 20, 2014

college algebra
It's already factored! Want to rephrase the question?
August 20, 2014

maths
what do meters have to do with anything? If the equation is 3 cos x = 25x, that's one thing. If not, fix the equation, but leave the m^2 out of it.
August 20, 2014

MATHH
The slope of the line joining those two points is (4+7)/(3-2) = 11 But, you are supposed to find the slope of any perpendicular line. That is -1/11.
August 20, 2014

math
1. reflect through the x-axis 2. reflect through (0,0) 3. a translation, but you are missing a sign.
August 20, 2014

math
You have a/b = 4/5 a/c = 6/11 You want b/c = (b/a)/(c/a) = b/a * a/c = 5/4 * 6/11 = 30/44 = 15/22
August 20, 2014

math
B gains 100 yards every minute. So, after 10 minutes, B has lapped A once. C gains 100 yards on B every minute, so after 10 minutes C has lapped B. Thus, after 10 minutes, A has gone 7 laps, B has gone 8 laps, C has gone 9 laps, and all are even again.
August 20, 2014

Math
-8 is less than any of them. All the negatives come first. The || values are all positive. So, (C) is correct
August 20, 2014

Geometry
In an equilateral triangle, the median is the same as the altitude. If the side is s, the median is √3/2 s. Each median extends from a vertex to the midpoint of the opposite side.
August 20, 2014

algebra
I get this far √a-√b = √18-√6 and have trouble figuring out what "nd multiply root5" means. How about filling in the rest using math symbols?
August 20, 2014

math
None are. They are, however, supplementary.
August 20, 2014

Maths
that would be 645.7/8 Drag out your calculator of choice to evaluate that quotient.
August 20, 2014

Algebra
D = 1.2√H Now just plug in H=12000
August 20, 2014

Trigonometry
Looks like time to review the basic trig functions. It always helps to draw a diagram. (1) 12.75/x = sin 48° (2) sin x = 3.1/9.4 (3) 16/x = tan 9°
August 20, 2014

Math
mi/hr * 1hr/60min * 1min/60sec * 5280ft/mi Note that the units all cancel out, leaving ft/sec Actually all of the factors will work, if you divide by 1mi/5280ft. However, since one usually wants to multiply, I'd say (d) would not be used.
August 19, 2014

math
y = x^3 All of the odd powers look basically the same as x^3. Play around at wolframalpha.com to see.
August 19, 2014

math
hmmm. Is it 4? Is 4^2 = 36? Does 4 have 3 as a factor? Better read what I wrote, and this time pay attention.
August 19, 2014

math
I'd make that 6, since 81 = 3^4. p^2 must have some powers of 3 in it, else GCF(p^2,81) = 1. GCF(36,81) = 9 9 would be better, but we needed an even integer.
August 19, 2014

English
none that I know of, but there are plenty which will correct your spelling of "grammar."
August 19, 2014

Physical Science
The airspeed is the speed relative to still air. In the absence of other factors, the airspeed is the same as the ground speed. If the wind is blowing, the wind velocity must be added to the bird's velocity in still air (airspeed), to get the velocity relative to the ...
August 19, 2014

physics
total distance: 108+42 = 150km total time: 6hr avg speed: 150km/6hr = 25 km/hr
August 19, 2014

math STEVE
you could have appended the correction to the original post. Anyway, 783-500 = 283 Apparently he makes no commission on the first $100. Assuming that, he makes 0% on 100 = 0.00 5% on 400 = 20.00 10% on 283 = 28.30 Total = 48.30 If I made a mistake on the first $100, make the ...
August 19, 2014

math
read it. The last sentence makes no sense.
August 19, 2014

math
#2. Assuming all the rest tried out for pitcher, then we have 1/8 + 1/3 + 1/4 = 17/24 So, the remaining 7/24 must have tried out for pitcher. #1 is garbled.
August 19, 2014

math
I did it this way 20*34 = 680 (total of all 20 numbers) 4*45 = 180 (total of the 4 numbers with mean 45) 680-180 = 500 (missing total, due to the other 16 numbers) 500/16 = 31.25 Your final answer is so huge it should have been a tipoff. The mean of the other 16 should have ...
August 19, 2014

math
6(y-7)-6 = 6y-48
August 19, 2014

math
no. my typo of 41 is a boo-boo, but your answer is correct. You correctly answered the question that was asked.
August 19, 2014

math
looks good. Does it work? Jack is 45 5 years ago, he was 41 40 = 46-6 OK
August 19, 2014

Science - go with DrBob
Dang. I forgot about the molecules, not atoms.
August 19, 2014

Science
you know Avogadro's Number, AN=6.023*10^23 Also, 1 mole occupies 22.4L (22400 cm^3) at STP. (a) (50dm^3)/(22400cm^3) * AN = ? (b) (10cm^3)/(22400cm^3) * AN * 19 = ? (because F has 19 nucleons/atom)
August 19, 2014

Math
(a) note that as x increases by 4, y increases by 2. Then, as x increases by 2, y increases by 1. (b) and (c) work the same way. Starting at the first point, note that the changes in y and x have the same ratio. That is, the slope remains constant, and since the middle point ...
August 19, 2014

Science
well, they would be nice to know, but the crew of the carrier would presumably include a doctor and weather guy. I'd pick D over A. Modern ships have lots of computers on board, and a knowledge of physics would come in handy in handling the ship.
August 19, 2014

math
using substitution, 7/y = 31-5/x so y = 7/(31-5/x) = 7x/(31x-5) 7x+5y=29xy y = -7x/(5-29x) 7x + 35x/(31x-5) = 29x * 7x/(31x-5) 7x(31x-5) + 35x = 203x^2 14x^2 = 0 As Damon noted, x=0 is not allowed, so there are no solutions. If you plot the difference between the two functions...
August 19, 2014

math
looks like (b) to me (a) is distributive
August 19, 2014

math
assuming both values are -1, even powers of -1 are +1 odd powers are -1 so we have -1 - +1 = -2 Or, you could factor out (-1)^1988 and have (-1)^1988(-1 - 1) = (+1)(-2) = -2
August 19, 2014

quadratic function
let x be the time since midnight, and y be the water level. We have y(11.75) = 0.46 y(23.50) = 0.46 the vertex is thus (17.625,2.16) Now you have three points, so you can determine the parabola, and you want x where y=1.
August 19, 2014

math
If the length is x, the width is x-.5 so x(x-0.5)=3 Now just solve for x
August 19, 2014

math
Hmmm. If you had said three more than twice its width, I'd have immediately said the room was 5x13. But, now we have to use some algebra. w(3w+3) = 65 w = 4.1815 for the perimeter, we want 2(w+3w+3)=39.452
August 19, 2014

algebra
I'll take a stab at it. As written, it appears to be (-1^2+11^2)(11^2- -7^2) (-1+121)(121- -49) (120)(170) 20400 If we assume the usual carelessness with parentheses, per Damon, then we have ((-1)^2+11^2)(11^2- (-7)^2) (1+121)(121-49) (122)(72) 8784 I can't believe you...
August 19, 2014

statistics
better check your dairy almanac for stuff like this.
August 19, 2014

Math
why is google like a search engine?
August 19, 2014

Math
depends on whom you ask Most say 5 rounds up Some say 5 rounds to the next even digit, so 35 rounds to 40 45 rounds to 40 Better check with your instructor or text to see which answer will get you marked correct.
August 19, 2014

Science
weight(N) = mass(kg) * 9.81 m/s^2
August 18, 2014

Advanced algebra
looks discrete to me
August 18, 2014

math
15*5+2 = 77 15*6+2 = 92 So, only two of them
August 18, 2014

Algebra 2
midway between the two extremes is (32.85+31.15)/2 = 32.00 So, |x-32.00| <= 0.85
August 18, 2014

Programming
read amount, months; show_deposit(amount,months); function show_deposit(amount,months) { deposit = amount/months; print deposit; }
August 18, 2014

maths
Hmmm. you are mixing up price per kg and per cob, with no indication of how many cobs per kg.
August 18, 2014

Maths
50-y You can easily do stuff like this if you use an actual number, and then study how you solved it. Suppose you had R50 and spent R10. What is the change?
August 18, 2014

Please Help ! Analytic Geometry
try this solution: http://www.jiskha.com/display.cgi?id=1408162681
August 18, 2014

Algebra
Not bad, except that 6.5-4 ≠ 1.5
August 18, 2014

Math
assuming the 2300 included the 15% profit, the value was 2300(0.85) Now divide that by 100 to get the per-share price.
August 17, 2014

Alegbra
you are correct. To see its graph, type that in at wolframalpha.com
August 17, 2014

math
assuming the smaller rectangle is enclosed by the larger, we have small rectangle: w(2w-1) large rectangle: (w+2)(2w-1+2) Assuming the shaded region is the difference between the two rectangles, we have (w+2)(2w+1)-w(2w-1) = 86 w = 14 So, the smaller is 14x27, with area=378
August 17, 2014

trig
since the spring starts at (0,-17), we know that D(t) = -17 e^-at cos(kt) since the period is 1/13, k = 26π and we have D(t) = -17 e^-at cos(26πt) Now, we know that the amplitude has decreased to (16/17)^(t/3) That means that a = -1/3 ln(16/17) = .02, and D(t) = -17 ...
August 17, 2014

geometry
Of course the 3rd side can be 5 or 9. That just makes an isosceles triangle. So, you want all the numbers n such that 4 < n < 14: 5+6+7+8+9+10+11+12+13 = 81
August 17, 2014

geometry
as a hint, suppose you joined the two sticks at the end. Now consider rotating the smaller one, from being end-to-end with the larger one, to overlapping it. What's the max and min possible length for the third side? Now list all the integers in that range and add 'em up.
August 17, 2014

geometry - again?
another of these triangle problems? Have any ideas of your own on this one?
August 17, 2014

physics - Go with Damon
As usual, go with Damon. He tends to think things through more carefully.
August 17, 2014

physics
as usual, s = 1/2 at^2 Since g is acting downward, the net acceleration is 32-9.8 = 22.2 m/s^2 upward s = 1/2 * 22.2 * 4.1^2 = 186.6m Actually, the question is poorly worded, since it implies that the net acceleration is 32 m/s^2, even after including the effects of gravity. ...
August 17, 2014

Pages: <<Prev | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | Next>>

Search
Members