# Posts by STEVE

Total # Posts: 51,184

**Math**

you want t such that 1550 * .9465^t = 825

**math**

three times as much But, lots of people use them the same way. If you are working on a problem, be sure to find out what was intended. "times" indicates multiplication "more than" indicates addition using them together always causes trouble.

**math**

huh? If you let u=cos(1/2x) then you just have 2u-u=0 clearly u=0 when is cos(1/2x)=0?

**math**

if the zeros are p,q,r then pqr=c

**math**

j/s = 30/40 j/d = 20/25 d/s = d/j * j/s = (25/20)(30/40) = 15/16 15/16 * 36 = $33.75

**Math**

ln(1/2) = -0.69314718 So, -.0001216 = 0.00017543ln(1/2) = ln2/5700 e^(-.0001216t) = e^(ln(1/2)*t/5700) = (1/2)^(t/5700) So, the half-life is 5700 years

**Math**

just using the first two data points, then in year t since 1990, you have y = 353 e^(kt), so 353e^(10k) = 375 That gives you k, so then you need to find when e^(kt) = 2

**math**

440/? + 28

**Math**

360/20 = ?

**math**

Note that 48^2+55^2=73^2 So, you have a right triangle...

**math**

f(x) = x^2 g(x) = ?(x+4) f(g) = g^2 = x+4 g^-1(x) = x^2-4 g^-1(f) = f^2-4 = x^4-4 g(f) = ?(f+4) = ?(x^2+4) g(f(x))+g^-1(f(x)) = ?(x^2+4)+x^4-4 for domain, just recall that ?u is defined only for u>=0 Then determine the range as usual.

**Math Help**

distance = speed * time

**Science unit 9**

Fill a jar with water. Submerge the ball and measure how much water spilled out.

**Advanced Functions**

(a) just plug and chug: 100(1+x/2)^20 = 300 (1+x/2)^20 = 3 1+x/2 = 3^(1/20) x = 2(3^(1/20)-1) = 0.1129 or 11.3% (b) See http://www.wolframalpha.com/input/?i=plot+y%3D100(1%2Bx%2F2)%5E20,+y%3D300+for+0%3C%3Dx%3C%3D0.12

**Geometry**

Draw an altitude from D to AB. It has length h. Let AB = x, AK=KD=y, BD=z since m?A = 60º, h=y?3 Now you have 4 equations in x,y,z,h: 2x+4y=24 x^2 = y^2+z^2 hx=2yz (area=base*height) h=?3 y Solve those and you will see that the parallelogram is a rhombus of side 6, with ...

**Designing Specialty Areas**

planes? Those babies are sharp, and easy to slice your hand with

**math**

Oops. I guess that is maybe ???

**math**

???

**math**

yes. The key is "more than 4"

**Calc**

Assuming you mean y = .2(9-x^2) Clearly, y(-4) ? -2 So, let's work with something like y' = .2(9-x^2) Then there will be families of arrows following trajectories of parabolas. You can find a nice online site at https://www.desmos.com/calculator/p7vd3cdmei Just type in...

**Math**

ever hear of google? Try looking for pentagon area

**Math**

can't read you attempts at fractions. Try something like 11 1/4 or 10 1/2 Consider using a regular pentagon with an apothem of 7", or the radius of the pizza. Look online to find the area of such a figure. It will be the smallest 5-sided box that will hold the pizza. ...

**Math**

Technically true, given the very poor wording of the question. But I think we can agree that we're looking for and answer of 20/4 = 5

**Math (Calculus II) (Graph approximation)**

(a) the graph is f', which is the slope of f. So, the slope at x=4 is on the graph, and appears to be -1 (b) sure it's possible. f(x) = ?f'(x) dx = "f(x)" + C where "f(x)" is the antiderivative of f'(x) So, f(2) can be anything you want, ...

**Maths**

rate of flow = volume/time

**Maths**

just substitute, since x=2y+3: (2y+3)^2 + y^2 = 18 Solve that for y, and then x=2y+3

**Maths**

an odd number is of the form 2k+1 where k is any integer. So, subtracting 2m+1 from 2n+1 you get (2n+1)-(2m+1) = 2n+1-2m-1 = 2n+2m = 2(n+m) any multiple of 2 is even

**Math**

Since we have no image, we cannot help. Why don't you try cutting out a triangle of the appropriate size, and see what you have to do to get it to line up with the other. If there's a scaling factor, make sure that you don't move the center of the triangle, and ...

**Algebra**

I don't mind answering the questions, but I don't like having to figure out what the question is, as well. I assume those three numbers are zeroes of the polynomial. So, by the Factor Theorem, the factors are y = (x+1)(x-2)(x+8)

**math**

figure out how many scores lie below 59 Turn that into a percent, and that gives the percentile. For example, if 42% of the scores lie below 59, 59 is in the 42nd %-ile.

**Math**

x/5 = 2/400 First, reduce 2/400 to 1/200 x/5 = 1/200 Now multiply both sides by 200 to get 40x = 1 x = 1/40

**science**

I hope some time in the last 6-7 hours you decided to spend 10 seconds with google, and found ... the term used to describe a species that influences the survival of many others in an ecosystem? The answer is Keystone Species

**Math**

#1,#2: the lines have different slopes, so they will intersect in one point #3 The lines are parallel, so they will not intersect at all. You should try graphing the lines to see what happens. If you don't have any graph paper, there are lots of online graphing sites.

**Math (Algebra 2)**

7/11 = 0.6363 77 is no kind of probability, as probabilities are always between 0 and 1. What were you thinking??

**Science---Hurry Please Help!**

yep

**Math**

think carefully. The next step is to subtract 8 from both sides.

**Physics**

google is your friend: https://en.wikipedia.org/wiki/Drop_(liquid)#Speed

**MATH: Check my answers | HELP ASAP!!**

correct

**Science**

Sorry. I just get annoyed when I see someone just guessing, with no apparent thought involved. Of all the possible answers, D is the most absurd, since the sun does not orbit the earth.

**Science**

NO - Try B The earth spins around completely every day, making the sun (in the sky) appear to go around from east to west! Geez.

**Science**

the orbit around the sun takes a long time. The sun's rise-fall happens every day.

**Physics**

(120m^3/min) * (1000kg/m^3 * 9.8) * 35m * (1min/60s) = ? W

**method of teaching maths**

google these topics, or look at existing texts.

**math**

I would parse it as the product of x and y: xy decreased by 2: -2 so, xy-2 The language is ambiguous. I guess a purist would say that the lack of a comma makes it mean x(y-2) and that the product of x and y, decreased by 2 would mean xy-2 Aren't you glad we use algebra ...

**maths parabola**

what's the trouble? The vertex is at (0,0), and tan(?/6) = 1/?3 so the line of the chord is y=x/?3 Now, see where the chord intersects the parabola: (x/?3)^2 = 4ax x^2/3 = 4ax x = 12a So, the length of the chord is ?((12a)^2 + 64a^2) = 4a?13

**MATH**

6^(3n) = 2^(3n) * 3^(3n) = 8^n * 27^n 9^(n+1) = 3^(2n+2) so you have 8^n * 3^(5n+2) = 8^n 3^(5n+2) = 1 = 3^0 5n+2 = 0 n = -2/5

**MATH**

FIND N: (6^(3n)*9^(n+1))/8^n=1

**Maths**

.80 = .15x

**Linear algebra**

z^3 = 27i z = 3?i i = 1 cis(?/2) ?i = cis((1/3)*(?/2 + 2k?)) for k=0,1,2 = cis ?/6, 5?/6, 9?/6 See http://www.wolframalpha.com/input/?i=z%5E3+%3D+27i

**Trigonometry**

This is the third time you've posted this question. See the related questions below. What seems to be the trouble?

**maths**

worst case: all 8 $1 coins drawn first. Then the 9th coin must be a $2 coin.

**physic**

(a) use the law of cosines: v^2 = 200^2 + 60^2 - 2*100*60*cos(80°) v = 198.6 km/hr at 2.7° N of E Now use that to break it into components.

**physic**

draw a diagram. (a) Ever hear of a 3-4-5 right triangle? (b) for this one, use the law of cosines to find the distance d: d^2 = 3^2 + 4^2 - 2*3*4*cos(120°)

**math**

not sure which face is the front, but clearly the point (3,6,4) lies on the plane x=3, and similarly for y and z.

**MATH**

think of a scaled-up 3-4-5 right triangle.

**Math**

(a) you have asked no question, but it appears you want to know when the height is 10 meters. (b) leaving your answer in the form shown, with no regard for operator precedence, is poor form.

**Decroly**

7 more, 2 less, 4 times, half of

**Math**

If you write them in the same form, you have x-2y = -3 x-2y = -3 so they are the same line.

**mushi**

To find c, use the law of cosines. cosc = cosa cosb + sina sinb cosC cosc = cos70° cos60° + sin70° sin60° cos89° c = 79° Now you can use the law of sines to find A,B.

**Advanced Functions**

by definition, f(f^-1(x)) = f^-1(f(x)) = x

**Geometry**

so the scale factor is 1 in : (12+4 in) = 1:16

**Math**

2.50a + 1.00(1300-a) = 1951 a = 434

**physics**

clearly the force is attractive, pointing toward the proton. F = kqq/r^2 = (8.99*10^9)(1.60*10^-19)^2/(4.30*10^-11)^2 = 1.24*10^-7 N

**physics**

? = 15rev/5sec = 3rev/s = 6? rad/s v = 20*2? cm/rev * 3rev/s = 120? cm/s

**physics**

since F = qq/r^2, changing r to 5r means you now have qq/(5r)^2 = qq/25r^2 = 1/25 * qq/r^2 = 1/25 F

**Math**

No value for x is needed. This is an exercise in recognizing the distributive property. 5(x+3) = 5*x + 5*3 = 5x+15 Now see what you can do.

**Science**

yes, but the sand is not part of it.

**Math**

how about some diagrams? Not available here. Interactive web sites don't translate well to a text-only site such as Jiskha. You would do well to remember that for circles, area = pi r^2 circumference = 2pi r

**math**

Since the ratios between terms is nowhere near constant, it is not exponential. If you look at the differences, they are always 2 or 3, so it is approximately linear.

**algebra invers mathod**

I have no idea what that weird double equation is, unless you might possibly mean to solve the system of equations 4x+y = 8 2x+3 = -1 that is clearly x = -2, y = 16 But that does not involve any "invers" method, so ...

**Math**

You think it is 3? Did you actually solve the equation to determine what it really is? Better yet, does the value 3 work in the equation? 2(1+3) ? 3+3 Bzzzt. Now it's time to do the math: 2(1 + x) = x + 3 2+2x = x+3 ... Now what do you think?

**Math**

in what context? It's just a number. Compared to a billion, it's not much. Compared to 1.5, it's pretty significant.

**Precalculus**

I'm sure your text includes the derivation of the formula that the rate of change of fg is ?(fg)/?t = f * ?g/?t + g * ?f/?t In this case, the rate of change of fg is thus 8*5 + 5*3 = 55 units/sec

**calculus**

The temperature T is the ambient temperature plus a steadily decreasing difference. In this case, T(t) = 15 + (23-15)e^(-kt) You can see that T(0) = 15 + (23-15)*1 = 23 that is the starting temperature. Now we are told that T(1) = 20: 15+8e^-k = 20 k = 0.47 So, T(t) = 15+8e^(-...

**math**

(32/13)*350 = 862

**math**

96*12^3 = 165888 cm^3

**Trigonometry**

Draw the base AX of the triangle, with AX nice and long. Draw angle A, making the other side nice and long. Mark C and drop an altitude to D on AB. Label the height CD=9 Now draw an arc of radius 15 centered at C, and you will see that it intersects AX at two points. Either of...

**Math**

1/2 of 1/2 = 1/2 * 1/2 = 1/4

**Algebra**

surely you know the radical indicates the "root": ?14 -- square root ?14 -- cube root ?14 -- fourth root etc.

**Maths**

well, how many hours passed? 2 degree drop every hour, starting at 10

**Maths**

A*0.08*7.5 = 1770

**calculus**

The way this is done is to express everything in terms of sin or cos: sin^3(?)cos^5(?) d? = sin^3? cos^4? cos? d? = sin^3? (1-sin^2?)^2 cos? d? Now let u=sin? du = cos? d? and you have u^3 (1-u^2)^2 du and it's a cinch...

**Algebra**

I don't know why you can't get it either, especially since you didn't show your work ... (26000-x)2813.95 + x(314.73)=26000(640.2) 73162700 - 2813.95x + 314.73x = 16645200 73162700 - 2499.22x = 16645200 2499.22x = 56517500 x = 22614.05559

**please help**

Don't let all those decimals scare you. Just do things as normal: -9.4(z-8)-4.1=5(z+2.5)-5.9 -9.4z + 75.2 - 4.1 = 5z + 12.5 - 5.9 -9.4z + 71.1 = 5z + 6.6 14.4z = 64.5 z = 64.5/14.4 ? 4.47917

**Math - Mean Value Theorem**

see the related questions below.

**Calculus**

Always draw a diagram for these problems. You will see that if the plane is x feet away from Maude's position, then tan? = 4500/x so, sec^2? d?/dt = -4500/x^2 dx/dt When ?=60°, that gives x = 2250, so 4 d?/dt = -4500/2250^2 * 22600 d?/dt = -226/45 ? -5.02 Of course, ...

**Math ASAP**

If by 33/ you mean ?33, then that is the irrational one, since 33 is not a perfect square. ?25 = 5, so that is rational.

**Math - calculus**

f'(x) = p x^(p-1) f(0)=0 and f(1)=1 So, you want c such that p*c^(p-1) = 1 Now just solve for c. For example, if p=2, f'(x) = 2x 2c = 1 c = 1/2 For p=3, 3c^2 = 1, c = 1/?3 so, the tangent line at x = 1/?3 is y = (1/?3)^3 = 1(x - 1/?3) or, y = x - 1/?3 + 1/3^(3/2) See ...

**algebra**

this would have been easy if you had used the proper units. The resistivity is ?-m So, you have (130m * 14.2?-m)/(A m^2) = 4.30? A = 429.3 m^2 That seems unlikely, so I looked up the resistivity of copper, and it is really 1.7*10^-8 ?-m Using that, we get A = 5.139*10^-7 m^2...

**Math**

There's nothing missing here. To solve for x, just follow the usual steps: e^(x+6) + 5 = 1 e^(x+6) = -4 No real solutions exist. Powers of e are never negative.

**Math**

you want t such that e^-.05t = 0.5 -.05t = ln(0.5) t = ln(0.5)/(-.05) = 13.86

**Algebra**

(-2t^2k)^2 = (-2)^2 (t^2)^2 (k)^2 = 4t^4k^2 Now you can see how to do the cube, right?

**Algebra**

Well, just factor it to see the zeroes: (m+3)(m-3)(3m+4)^2

**Algebra 2**

It's a parabola. Just google conic sections for various discussions. Wikipedia might be a good place to start: https://en.wikipedia.org/wiki/Conic_section

**Algebra**

the length is 6 more than the width, so w(w+6) = 216

**Calculus**

The distance z from (2,1/2) to (x,x^2) is z = ?[(x-2)^2 + (x^2 - 1/2)^2] = 1/2 ?(4x^4-16x+17) dz/dx = 4(x^3-1)/?(4x^4-16x+17) dz/dx=0 at x=1 z(1) = ?5/2 Or, consider the line through (x,x^2) and (2,1/2). It has slope (1/2 - x^2)/(2-x) The tangent line to y=x^2 has slope 2x. So...

**Geometry**

?(78/128) ? 0.78 It is an odd scale factor, but that's life.

**math - algebra**

?(1/81) = ?(1/3^4) = 1/3

**Mat222**

(s-t) = (x-3)-(3x+1) = -2x-4 (s.t) = (x-3)(3x+1) (s+t)(-2) = s(-2)+t(-2) = -5 + -5 = -10 or, (s+t)(x) = (x-3)+(3x+1) = 4x-2 so (s+2)(-2) = 4(-2)-2 = -10

**Algebra**

(b*(b-4))/2 = 86