Sunday

February 26, 2017
Total # Posts: 48,810

**Precalculus**

since cos(4t) has period pi/2 and sin(6t) has period pi/3 the LCM is pi

*January 29, 2017*

**math**

36/720 = 1/20 = 5% absent. So, ...

*January 29, 2017*

**Math**

this is just a right triangle with longest leg length 4. (Hypotenuse is 5) 5+3+4 = 12 180/12 = 15 So, scale it up by a factor of 15, and its sides are 75:45:60

*January 29, 2017*

**math2**

just use the power rule. For example, a. v(t) = 2t+3 v(2) = 2*2+3 = 7

*January 29, 2017*

**Math**

?(-3/2 * 81) = 9?(3/2) i ?(-3/(2*81)) = 1/9 ?(3/2) i = 1/(3?6) i = 1/18 ?6 i

*January 29, 2017*

**maths**

how far have you gotten using Reiny's suggestion? For #2, you might also look at it as involving the translation of one line onto a parallel line. The line from (-2,3) to (3,4) is one side of the parallelogram. If you translate (-2,3) to (-3,-2) then you have moved it by...

*January 28, 2017*

**Pre Cal 12**

900(1+r/4)^(4*12) = 1400 r = .0369 ? 3.7%

*January 28, 2017*

**Pre Cal**

f(x) = (x-3)^2(x-2)+c Note that 3^2*2 = 18 But that will be -18 (why?), so c=36 and that's "constant" not constance.

*January 28, 2017*

**Calculus can you please show me the step by step s**

As Tom showed you, I = A/s^2 + 8A/(600-s^2) Actually, that is not quite right. It should be 1/s^2 + 8/(600-s)^2 You should have caught that. In any case, The A is just a constant, so it does not affect the solution, and we can say I = 1/s^2 + 8/(600-s)^2 dI/ds = -2/s^3 + 16/(...

*January 28, 2017*

**Math**

|T-88| <= 7.5 88-7.5 <= T <= 88+7.5 ...

*January 28, 2017*

**Maths**

well, 2x = 25-5y So, use that: 4x-3y = 11 2(2x)-3y = 11 2(25-5y)-3y = 11 50-10y-3y = 11 -13y = -39 y = 3 Now use that to find x.

*January 28, 2017*

**Math show work**

Using convenient units of 1 AU for earth orbit and mass of sun=1, and P=1 earth year, you know that R^3 = P^2 using 11.1P, (11.1P)^2 = 123.21P^2 = (4.976R)^3 So, the distance is 4.967 AU

*January 28, 2017*

**Math**

recall that cot -x = -cotx = -1/tanx

*January 28, 2017*

**Math**

well, ? radians = 180 degrees 4.5 rad * 180deg/? rad = ? deg

*January 28, 2017*

**Mean (Average) Question**

How come you have only 9 values, if you have ten lions? Surely the 10th litter is also zero? In any case, the mean is the sum divided by the no. of values being measured.

*January 28, 2017*

**Geometry and shape**

Or, any regular n-gon with more than 4 sides and n an even number.

*January 28, 2017*

**math**

ar^3/ar^11 = 1/256 1/r^8 = 1/256 r = 2 Now you can find a, so the sum S8 = a(2^8-1)/(2-1) = 127a

*January 28, 2017*

**math**

r^2 = 2^2+9^2 = 85 so, if the unknown chord is 2x in length, 6^2+x^2 = r^2

*January 28, 2017*

**Maths**

If x is the son's age, 9x+15 = 3(x+15)

*January 28, 2017*

**Math**

#2 Huh? The planetary radius is equal to the separation? Do the planets touch, or is the separation between planetary surfaces? If so, then a cube with side 5r contains about 9 planets of radius r. So, the void ratio would be ((5r)^3 - 9*4/3 ?*r^3)/(9*4/3 ?*r^3) = (125-12?)/12...

*January 28, 2017*

**Math**

#1 You know that the weight is GMm/r^2 = 100 Replace M by 7M and r by 2r, and you have the new weight of G(7M)m/(2r)^2 = 7/4 GMm/r^2 = 175

*January 28, 2017*

**Math**

not quite sure what you're after, but d/dx (x^3) = 3x^2 d/dx (x^2+x) = 2x+1 If you want x where they are equal, then 3x^2 = 2x+1 3x^2-2x-1 = 0 (3x+1)(x-1) = 0 x = -1/3 or 1

*January 28, 2017*

**Math**

You have not asked a question. Clearly, to wrap all 80 boxes, you need 80 * 2 3/4 = 220 ft of ribbon. Now you have to decide just what it is you want to know...

*January 28, 2017*

**Math**

which region is shaded? Are the circles concentric? The area of the larger circle is 81?. The smaller circle has area 121?/4 = 30.25?

*January 27, 2017*

**Math -**

8x + 14y = 24 6x + 7y = 10 double the 2nd equation and you have 8x + 14y = 24 12x + 14y = 20 Now if you subtract the top from the bottom, the 14y cancels and you have 4x = -4 x = -1 Now use that in either original equation to find y: 8x+14y = 24 8(-1)+14y = 24 -8+14y = 24 14y...

*January 27, 2017*

**Basic math**

42.42

*January 27, 2017*

**basic calculus**

dA = 8?r dr dr = -1/2, so dA = 8?*200*(-1/2) = -800? m^2 so, the area is approximately 4?*200^2 - 800? = 159200?

*January 27, 2017*

**Pre Cal**

You know A, since A+B+C=180 a/sinA = b/sinB ...

*January 27, 2017*

**Math**

A\B is all x in A but not in B x not in A\B is all x in A&B or in B. So, A\(A\B) is all x in A and in (A&B or B) so, it is all x in A&B ? B

*January 27, 2017*

**Math**

The legs add up, but the eyes do not. You are correct that there are 19 animals. But then you go on to finish wrong. If there are m cows (moo) and c hens (cluck), 4m+2c = 52 2m+2c = 38 2m = 14 m = 7 7 cows and 12 chickens 7*4+12*2 = 28+24 = 52 legs 2*(7+12) = 2*19 = 38 eyes

*January 27, 2017*

**Math**

90 by 60

*January 27, 2017*

**Math**

Not sure how to parse your expression. B(A\B) is not correct syntax, since B is a set (A\B) is a set, call it C So, what does BC mean? Similarly, (A\B) is a set, so call it D. Again, what is DC? two set names juxtaposed has no meaning.

*January 27, 2017*

**Algebra - units**

Damon makes a good point. You know that you can always multiply by 1 without changing anything. If 6 meters = 1 minute, then 6m/1min = 1 1min/6m = 1 Those "conversion factors" are just different ways of writing 1! If you pick the correct expression, the unwanted ...

*January 27, 2017*

**Maths**

p+g+c = 100 100p+30g+5c = 1000 A little checking will show that he bought 94 chickens 1 goat 5 pigs

*January 27, 2017*

**ALGEBRA MATRICES HELP**

Turn to the section in your text. Start reading.

*January 27, 2017*

**algebra**

sounds good to me.

*January 27, 2017*

**Math**

well, four pounds more than three times the weight of his sister becomes 3w+4 so, now what do you think?

*January 27, 2017*

**Math**

well, each side is ?6.25 = 2.5 km, so since there are 4 sides, ...

*January 27, 2017*

**Maths**

see related question below

*January 27, 2017*

**math**

draw a diagram, including a diameter perpendicular to the chords. You will find a couple of 8-15-17 right triangles.

*January 27, 2017*

**Precalculus**

I think I can read this as z^7 = 1/?2 - 1/?2 i so, that means z^7 = cis 315° z = cis(315/7)° = cis45° + k*360/7 for k=1..6

*January 27, 2017*

**Maths**

If they work 3/2 as fast, it will take 2/3 the time.

*January 27, 2017*

**algebra**

clearly, when -16t^2 + 156t + 105 = 0

*January 26, 2017*

**Math**

h * h/2 * 1/2 = 100 h = 20

*January 26, 2017*

**Math**

well, 8 pts = 1 gal, so ...

*January 26, 2017*

**trig**

sin? = y/r cos? = x/r tan? = y/x tan? is the slope, so you have tan? = 5 r^2 = x^2+y^2 = 26

*January 26, 2017*

**Math**

it appears so.

*January 26, 2017*

**Trig**

csc^2 ? = 1+cot^2 ? so, ...

*January 26, 2017*

**Algebra**

a = 7 d = 3 Now you can answer the questions: T8 = a+7d Sn = n/2 (2*7 + (n-1)*3) > 425

*January 26, 2017*

**formal language**

ok. and ... ?

*January 26, 2017*

**8th grade math**

hmmm. I don' see no steenking triangles!

*January 26, 2017*

**math**

t = 2s k = t-3 t+s+k = 37

*January 26, 2017*

**Math**

so, we have (1,9) -> (3,-3) (3,12) -> (5,-6) (4,4) -> (6,2) x -> x+2 y -> 6-y = 3-(y-3) So, shift right 2 reflect across the line y=3.

*January 26, 2017*

**Math**

time = distance/speed, so time for sound to return: d/c time to fall: t = T-d/c d/c + gt^2/2 * d/t = T now just solve for d

*January 26, 2017*

**algerbra**

Looks like A to me. The prices are in the ratio 1:3:5:7, just like the times.

*January 26, 2017*

**Math**

450/(600+450+270) = 15/44

*January 26, 2017*

**math**

12^2 + L^2 = 20^2 L = 16 It's just a 3-4-5 triangle scaled up by a factor of 4.

*January 25, 2017*

**Trigonometry**

sin? = 1.2/4.4

*January 25, 2017*

**Calculus**

#1 correct ?[1,4] ?(1 + 1/4x) dx ?[1,2] ?(1+4y^2) dy where did you come up with [16,1]? The curve goes from (1,1) to (4,2) Note that ?(1+4y^2) is NOT (1 + 2y) ?(a^2+b^2) is not a+b !! #2. looks ok. For C, the radius is just x+2 For D, the radius is just 3-y

*January 25, 2017*

**Math**

use your standard conversion factors for gal/L and mi/km

*January 25, 2017*

**Measurement**

u = 10^-6 p = 10^-12 you surely have a list of prefixes - use them.

*January 25, 2017*

**Algebra**

you know that x = 3y-6 So, use that in the other equation: 20y + 35(3y-6) = 3795 20y + 105y - 210 = 3795 125y = 4005 y = 32.04 Now use that to find x. Odd, I expected an integer answer. Check for typos.

*January 25, 2017*

**Algebra 1**

just evaluate at x=5

*January 25, 2017*

**Trigonometry with right triangles**

you can always get a book on geometry and study it. I learned calculus on my own from my teacher's textbook. But I suggest you finish Algebra I before trying geometry or trig. It will give you a good foundation to work with.

*January 25, 2017*

**Trigonometry with right triangles**

what, you can't figure 90-25 ?

*January 25, 2017*

**Trigonometry with right triangles**

cos(x) = sin(90-x) That's what the co- in cosine means: sine of the complement.

*January 25, 2017*

**Algebra 2**

I get B. What did you do? Maybe we can figure what went wrong.

*January 25, 2017*

**Calculus**

sin = y/r cos = x/r sinx = 1/5 cosx = -?24/5 = -2?6/5 cosy = 1/8 siny = ?63/8 = 3?7/8 I'll do sin(x+y) and you can apply the formulas for the rest. sin(x+y) = sinx cosy + cosx siny = (1/5)(1/8)+(-2?6/5)(3?7/8) = 1/40 - 6?42/40 = (1-6?42)/40 makes sense, since x+y is in QIII

*January 25, 2017*

**Algebra**

If the walkway has width w, then 2(6+2w + 10+2w) = 60.8

*January 25, 2017*

**maths**

a = 31 1/4 = 125/4 ar^(n-1) = 2 r^(n-1) = 8/125 Now, 8/125 = (2/5)^3 Looks to me like r = 2/5 and n=4 and the sequence is thus 125/4, 25/2, 5, 2 I think you'll find it adds up to 203/4

*January 25, 2017*

**Algebra**

Draw a diagram. Set the center of the ellipse at (0,0). Then we have semi-axes a = 74 b = 48 x^2/74^2 + y^2/48^2 = 1 Now plug in y=10 and find x. The distance d is then d^2 = x^2 + 10^2

*January 25, 2017*

**calculus**

3xy^3+4xy=63 3y^3 + 9xy^2 y' + 4y + 4xy' = 0 y'(9xy^2+4x) = -(3y^3+4y) y' = -(3y^3+4y)/(9xy^2+4x) So, at (9,1) y' = -7/117 Now you have a point and a slope, so the line is y-1 = -7/117 (x-9) Refer to http://www.wolframalpha.com/input/?i=plot+3xy%5E3%2B4xy%...

*January 25, 2017*

**Math 114**

so, did you check? 3+9=12 so, ok.

*January 25, 2017*

**MATH**

well, 4 for each kg, so ...

*January 25, 2017*

**math**

72/4 = 18 So, multiply all the lengths by 18 to get 54+72+36 = 162

*January 25, 2017*

**Math**

-8+3 = -5

*January 25, 2017*

**math**

1/5 boys absent means 4/5 present 4/5 boys = 160 = 4*40 So, there are 5*40 = 200 boys 2/5 of the students are boys 200 = 2/5 * 500 So, there are 500 students in all. Now you can see how many are girls.

*January 25, 2017*

**Trigonometry with right triangles**

Since <DEF is 60° and DE = ?2, EF=?6. So, the area is (?2*?6)/2 = ?3 Rather than all this *line in between answer D* stuff, you could have just written ?3/?2

*January 25, 2017*

**trigonometry**

If the pedestrian is x meters from the short building, 10/x = tan20°10' the distance to the tall building is 40-x You don't seem to care how tall the other building is, but if the tall building has height h, then (h-10)/40 = tan15°20'

*January 25, 2017*

**complex number help**

?-16 = ?(16 cis ?) = ?16 cis ?/4 = 2(1/?2 + 1/?2 i) = ?2 + ?2 i That is the 1st root. There is an equivalent root in each quadrant. See http://www.wolframalpha.com/input/?i=x%5E4+%3D+-16 Work the 5th root the same way, using de Moivre's theorem.

*January 25, 2017*

**maths**

assuming that the wood purchased will be used efficiently, the volume of wood is the outside volume less the inside volume. Since there are parallel sides, the inner dimensions are 5 cm less than the outer. Thus, the volume of wood is (200-5)(120-5)(75-5) = 1569750 cm^3 = 1....

*January 25, 2017*

**MATH**

x^2 * x^2 = (x*x)*(x*x) = x*x*x*x = x^4 or, x^2 * x^2 = x^(2+2) = x^4 or, x^2 * x^2 = (x^2)^2 = x^(2*2) = x^4

*January 25, 2017*

**Math**

f(5/2) is the remainder when f(x) is divided by (x - 5/2) This site can help: http://calc101.com/webMathematica/long-divide.jsp

*January 24, 2017*

**Math**

see http://calc101.com/webMathematica/long-divide.jsp

*January 24, 2017*

**Math**

well, (8-5)^2 = 3^2 = 9 I assume you can take it from there ...

*January 24, 2017*

**Calculus**

a little synthetic division will show that f(x) has roots in (-2,-1) and (0,1).

*January 24, 2017*

**Calculus**

F'(-4) = lim(h->0) [((-4+h)^3 + (-4+h)^2) - ((-4)^3+(-4)^2)]/h = lim(h->0) [(h^3-11h^2+40h-48)-(-48)]/h = lim(h->0) (h^3-11h^2+40h)/h = lim(h->0) (h^2-11h+40) = 40

*January 24, 2017*

**Calculus**

secx = 2 or -2 or, cosx = 1/2 or -1/2 One root in each quadrant.

*January 24, 2017*

**Calculus**

The slope of the line is (30000-280000)/10 = -25000 So, V(t) = 280,000 - 25,000t

*January 24, 2017*

**Math**

A - 1/2a = P

*January 24, 2017*

**Physics (9th)**

sorry. 26.39/4 = 6.59 don't know how I got so far off. So, fix t and redo the calculation...

*January 24, 2017*

**Physics (9th)**

recall that the equation for distance is s = vt + a/2 t^2 95 km/hr = 26.39 m/s So, it will take 26.39/4 = 6 seconds of braking to stop. s = 95*7 - 2*6^2 = 593 meters to stop I guess she had good eyes, seeing an antelope at half a km away! Or, maybe she just hit it, or swerved ...

*January 24, 2017*

**Algebra**

p = 3b-6 20b+35p = 3790 Now just solve for b and p to see how many of each there are.

*January 24, 2017*

**Math**

correct

*January 24, 2017*

**Math**

oops 47+30 = 77 > 70

*January 24, 2017*

**Math**

well, 70-47 = 23 so, any number bigger than 23 will make the statement true 47+30 = 73 > 70 I have no idea what outlandish method they taught to solve the problem.

*January 24, 2017*

**chem**

impatient much? see your other post...

*January 24, 2017*

**chem**

29 moles of O2 --> 58 moles of H2O So, how many grams is that?

*January 24, 2017*

**find the equation**

review the point-slope form.

*January 24, 2017*