Sunday
August 28, 2016

Posts by steve

Total # Posts: 42,827

maths 114
area of circle minus area of minor segment.
July 13, 2016

math
(x-1)y" + 2y' = 0 If we expand about x=0, we assume y = ∑anx^n y' = ∑nanx^(n-1) y" = ∑n(n-1)nx^(n-2) Plug these into our DE and we have (x-1)∑n(n-1)nx^(n-2) + 2∑nanx^(n-1) = 0 ∑n(n-1)nx^(n-1) - ∑n(n-1)nx^(n-2) + 2&#...
July 13, 2016

Math
well, since 3 = 18/6, the cost is X/6
July 13, 2016

math
well 64πh = 384π
July 13, 2016

maths
6cis 5π/6 * 3cis 4π/5 = 6*3 cos(5π/6 + 4π/5) = 18 cis 49π/30
July 13, 2016

analytic geometry
since (8,0) divides the line into a proportion, (8-x)/(10-x) = (0-7)/(y-7) y = 14/(x-8) There are many possible lines. A few possibilities are x=9, y=14 x=10, y=7 x=15, y=2 x=22, y=1 x = -6, y = -1 x = 1, y = -2 x = 6, y = -7 x = 7, y = -14
July 13, 2016

math
t = 2-x, so y = 1+2(2-x) = 5-2x At t=0, we have (2,1)
July 13, 2016

Math
If x is the original number, x/24 = x-16 Comes out a fraction. If, on the other hand, you meant to say he got a quotient which was 16 less than the correct quotient, then we have x/24 = x/12 - 16 x = 384 I suspect you have garbled the question.
July 13, 2016

Maths - duh
Stupid me. I read the question as "two equal parts" and wondered what the fuss was about. Clearly the ratio would be 1:1 Nice catch, Reiny.
July 13, 2016

Maths
what do you mean by "their areas"?
July 13, 2016

math
it has to make up 130 miles in 3 hours. So, its speed is 65 + 130/3 mi/hr
July 13, 2016

pre-calculus
well, for 30° it is (1/2, √3/2) Now move that around 180°
July 13, 2016

computer sc.
no diagrams, but the steps are n=50 i=0 sum=0 get score i += 1 sum += score i<n? If so, repeat avg = sum/n
July 13, 2016

Pre Calculus
or, more directly, using deMoivre: 8cis10 * 5cis200 = 8*5 cis(10+200) ...
July 13, 2016

math
just plug in the numbers where F = 9/5 C + 32
July 13, 2016

math
speed = distance/time, so 1.4km/1.667hr = 0.84 km/hr or, using fractions, (7/5)km/(5/3)hr = 21/25 km/hr
July 13, 2016

Algebra
6/20 --------- = 2/5 3/4
July 12, 2016

Math
y = a(x+3)(x+1)(x-4) at x = -2, (x+3)(x+1)(x-4) = 18 so, y = 4/3 (x+3)(x+1)(x-4)
July 12, 2016

Pre-Cal
Draw your triangles in standard position. Then it is clear that sinx = -4/5 tanx = 4/3 cosy = -√77/9 tany = -2/√77 Now just plug the needed values into the identities you have
July 12, 2016

Pre-Cal (Help Please!!!!)
#1 cosθ (3tan^2θ - 1) = 0 so, cosθ = 0 or tanθ = ±1/√3 Those are standard familiar values, right? #2 tan3θ = -1 3θ = 3π/4 or 7π/4 + n*π/3
July 12, 2016

Math
Just factor as usual: 2x + 9√x - 5 = 0 (2√x-1)(√x+5) = 0 √x = 1/2 x = 1/5 √x = -5 no solution there
July 12, 2016

Algebra
just expand and equate coefficients 4x^2+20x+r = 4x^2+4sx+s^2 4s=20 s=5 r = s^2 = 25 r-s = 20
July 12, 2016

Physics
F = ma, so a = F/m = 18N/6kg = 3 m/s^2 v = at = 3*5 Now you try the other. Same ideas.
July 12, 2016

maths studying for pre cal test
draw angle A and side b. Now, if it were a right triangle, with b the hypotenuse, side a would be the altitude, of length 14 sin60° = 12.12 So, you see, a little side a of length 4 will not reach down the the base, AB. If C is the right angle, that means that tanA = 6/14, ...
July 12, 2016

Studying for math test
Read the question carefully. It said which of the following is not equivalent? Actually, both c & d are not
July 12, 2016

Studying for math test
take a look at the related questions below. In particular, http://www.jiskha.com/display.cgi?id=1468255540
July 12, 2016

12th grade chemistry
normalbold
July 12, 2016

12th grade chemistry
<pre> abc def ghi jkl </pre>
July 12, 2016

12th grade chemistry
<font size="4">size 4</font> <font size="2">size 2</font>
July 12, 2016

12th grade chemistry
abc<small>abc</small>
July 12, 2016

science
well, p = mv plug in your numbers and solve for v.
July 12, 2016

chemistry
note that each 2 moles of KOH produce 1 mole of Mg(OH)2. So, how many grams in 2 moles of magnesium hydroxide?
July 12, 2016

MATHS
42°
July 12, 2016

MATHS
3x+A=45 x = (45-A)/3 Is there something else you want to specify?
July 12, 2016

Math
or, differentiating y' directly, y" = 50y^3(-5xy^2+20xy+18)/(10xy+9)^3 y"(1,1) = 50(-5+20+18)/19^3 = 1650/6859 which agrees with Reiny's result above!!!
July 12, 2016

physics
How long does it take the bomb to fall 8000m? 4.9t^2 = 8000, so t=40 s In 40s, the bomb will travel 8000m. What a coinkidink! So, the angle is just 45°
July 12, 2016

math
just solve 3x + 1/2 x^2 = 8
July 12, 2016

pre cal
splashdown occurs when h=0 max height is at t = -b/2a = 115/9.8
July 12, 2016

agebra
well, if you know the mean and the std, µ-2σ <= x <= µ+2σ
July 12, 2016

math
dy/dx = xy dy = xy dx dy = 1*2 * 0.4 = 0.8
July 12, 2016

pre cal
recall that the vertex of a parabola is at t = -b/2a so evaluate h(t) there.
July 12, 2016

maths
Just change the numbers in Reiny's solution here: http://www.jiskha.com/display.cgi?id=1455402753
July 12, 2016

pre cal
well, the diagonal of the square is the diameter of the circle...
July 12, 2016

pre cal
The time it takes for the sound to come back is d/c The time it takes to fall a distance of d is found using h0 + v0 t - g/2 t^2 = d Solve that for t, and then you have t = 1/g (v0 + √(v0^2 - 2g(d-h0))) Now you know that 1/g (v0 + √(v0^2 - 2g(d-h0))) + d/c = t Now ...
July 11, 2016

Algebra/Calculus
note that (x+y)^2 = x^2+2xy+y^2 x^3 + y^3 = (x+y)(x^2-xy+y^2) Now just plug in what you know.
July 11, 2016

algebra 2
3x-15 = 0 when x=5 everything else is ok.
July 11, 2016

algebra 2
a denominator cannot be zero because division by zero is undefined. For this one, 64 is never zero.
July 11, 2016

Pre-Cal
recall that tan(x+y) = (tanx + tany)/(1-tanx*tany) so, cot(x+y) = (1 - tanx tany)/(tanx + tany) Now divide top and bottom by tanx*tany sinx(cotx+tanx) = sinx(cosx/sinx + sinx/cosx) = cosx + sin^2x/cosx = (cos^2x + sin^2x)/cosx = secx
July 11, 2016

algebra
ok
July 11, 2016

MATH
As I said earlier, e^(a+b) = e^a * e^b That means that e^(a+b+c) = e^a * e^b * e^c Now just plug in your values for a,b,c.
July 11, 2016

Pre-Cal
Looks ok to me. It might be easier to read π/6 + nπ 5π/6 + nπ So, plug in various values of n to get all the solutions in [0,2π) There will be four of them
July 11, 2016

math please help?! studying for test!!
√(81+x^2) = √(81+81tan^2θ) = √(81(1+tan^2θ)) = √(81sec^2θ) = 9secθ Looks like you need to brush up on your basic trig identities.
July 11, 2016

math help?!
36-x^2 = 36-36sin^2θ = 36(1-sin^2θ) = 36cos^2θ so, √(36-x^2) = 6cosθ
July 11, 2016

Pre-Cal (Help Plz!)
so, you got tanθ = ±√3 cosθ = -1/2 tanθ = √3 means θ = π/3 or 4π/3 tanθ = -√3 means θ = 2π/3 or 5π/3 cosθ = -1/2 means θ = 2π/3 or 4π/3 so, that gives nπ + π/3 nπ + 2...
July 11, 2016

Pre Calculus
Hmmm. I get cosu*cosv - sinu*sinv = (-24/25)(-12/13)-(7/25)(5/13) = 288/325 - 35/325 = 253/325
July 11, 2016

Pre Calculus
since y>0 and x<0, draw your triangles, and you can see that cos u = -24/25 sin v = 5/13 Now just plug them into your cos(u+v) formula.
July 11, 2016

MATH
yes, as far as you went. But, if you are using natural logs, log(e) = 1, so the answer is just 5y By definition logbb^n = n b^(logbn) = n because logs and powers are inverse functions, just like √x and x^2 are inverses. Like + and - or * and / It's just that we don&#...
July 11, 2016

MATH
recall that e^(a+b) = e^a * e^b AND LOSE THAT CAPS!!
July 11, 2016

maths
"square bracket"? Is your keyboard defective, so you can't just type "[" ? Even more confusing is that you didn't use what I gave you at http://www.jiskha.com/display.cgi?id=1468255629
July 11, 2016

Pre-Cal
you know that the reference angle is θ = π/3, right? Because cos π/3 = 1/2 Now, since cosπ = x/r, you need x negative, so you are in QII and QIII. So, draw your triangle on the negative x-axis, giving you π-π/3 and π+π/3 = 2π/3 and ...
July 11, 2016

Analytic geometry
Using what I gave you here: http://www.jiskha.com/display.cgi?id=1468252134 you can surely figure the rest, no? Heck, I even showed you the graph! Where do you get stuck?
July 11, 2016

math
Not unless 7-1 = 8
July 11, 2016

Math
If what you have is 0.5(x-2)^2 ------------------- (x+1)(x-5)^3 then you have 0.5(x^2+...) / (x^4+...) which approaches zero for large values of x.
July 11, 2016

pre calculus
No. You are half right. θ=12x is the right substitution to use, but if θ = 12x, what you have is cos(θ/2) = cos 6x
July 11, 2016

pre calculus
did you even look up your half-angle formula? It says that cos(θ/2) = √[(1+cosθ)/2] I think the substitution is now clear.
July 11, 2016

maths
recall that 2 sin x/2 cos x/2, so the equation becomes cos x/2 - 2 sin x/2 cos x/2 = 0 cos x/2 (1 - 2sin x/2) = 0 I think you can handle that, right?
July 11, 2016

math
but a triangular pyramid does: v = 1/3 Bh Now just plug in your numbers.
July 11, 2016

maths
you telling me or asking me? Naturally, sin(2x) is not one of your answers, but if you let x = π/10 and you plug that in, I bet it is one of your answers.
July 11, 2016

maths - Oops
Dang! That is sin(2x) = 2 sinx cosx
July 11, 2016

maths
look up your formulas. You want 2 sin(a) cos(b) = sin(a+b) cos(a-b) You don't even need the product-to-sum formulas, since your double-angle formula says that cos(2x) = 2 sinx cosx
July 11, 2016

math
so, did you do it? what did you get? try wolframalpha.com http://www.wolframalpha.com/input/?i=sin+2x+%2B+1.5+cos+x,+0%3Cx%3C2pi
July 11, 2016

Pre Calculus
you know that sin^2 x + cos^2 x = 1, so when you expand you have sin^2 x + 2 sinx cosx + cos^2 x recall also that sec^2 x = 1 + tan^2 x cos(pi/2-x) = sin(x) So, what do you think?
July 11, 2016

Math
assuming you mean a parabola, recall that x^2 = 4py has axis x=0 directrix at y = -p latus rectum = 4p So, your equation is (x-2)^2 = 4(y-4) see http://www.wolframalpha.com/input/?i=parabola+(x-2)%5E2+%3D+4(y-4)
July 11, 2016

Math
If there are x math problems, then we know that (4/5) x + 3 = 53
July 11, 2016

math
well, we know that the number is between 5500 and 6500 There must be many possibilities: 5579 5588 5597 ... 6497 6488 6497
July 11, 2016

geometry
the exterior angles of an n-gon add up to 360 degrees.
July 11, 2016

Math
I can only think of 2 and 14 which work
July 11, 2016

pre cal
C'mon, this is just Algebra I: f(x) = a(x-41)(x-p)
July 11, 2016

Math
V = k/P So, PV is constant. You want P such that P*160 = 30*240
July 11, 2016

math
clearly the plant grows at 1/2 cm/week So, you have a slope and a point (0,2) ...
July 11, 2016

pre cal
for x not -1 or 1, put it all over a common denominator, and you have 3x^2-2x-3 = 0 I'm sure you can handle that.
July 11, 2016

Math
63 <= 2(w + w+4) <= 95 63 <= 2(2w+4) <= 95 63 <= 4w+8 <= 95 55 <= 4w <= 87 13.75 <= w <= 21.75 so, the maximum width is 21 That makes the max length 25
July 11, 2016

pre cal
or, just factor it: (√x-2)(2√x-1) = 0 √x = 2 or 1/2
July 11, 2016

chemistry
First balance the equation. The product has a ratio of 1:3 for the atoms. So, 2Cl2 + 6Fl2 = 4ClF3 convert to moles of each reactant The one with the lesser no. of moles needed will limit the reaction. Then figure how many moles of product are produced, and go back to grams.
July 11, 2016

MPA
so, did you do some searches? geez, you can do that at least, right?
July 11, 2016

chemistry
so, do you know what reaction yield means?
July 11, 2016

Maths Year 10 Equations
c(x) = 2100/x s(x) = c(x)+8 = 2100/x + 8 extra credit: how much money did he make on the sales?
July 11, 2016

math
surely you can see that T(k) = 20+5k
July 11, 2016

Calculus
well, surely you must in fact have done some work. rather than mumble some excuses, why not show what you did? Then we can analyze it for accuracy and presentability. The critical numbers are where f'(x) = 0 or f'(x) is undefined. So, what does that give you?
July 11, 2016

Calculus
to find the absolute max/min, you need to check for local extrema in the interval. Then check f(x) at the ends of the interval to see whether they qualify as being more max/min. f'(x) = 2/∛(x-2) clearly that is never zero, so there are no internal local extrema. So, ...
July 11, 2016

maths
well, come on. How many pairs of digits are there that add to 9? Also, you know that the first digit is greater, since reversing the digits makes a smaller number.
July 11, 2016

Physics
Recall that the range is r = v^2/g sin(2θ) so, plug in your numbers and solve for θ.
July 10, 2016

math,maths
(x+2)/x >= 1/5 If x>0, x+2 >= x/5 4x/5 >= -2 x >= -5/2 So, x > 0 If x<0, x+2 <= x/5 4x/5 <= -2 x <= -5/2 So, x <= -5/2 So, in interval notation, x is in (-∞,-5/2]U(0,∞)
July 10, 2016

Math
p(x) = 9x - (3x+4700)
July 10, 2016

Math
Draw a Venn diagram. It is clear that 800-(400+240-B&S) = 160+B&S = 200 B&S = 40
July 10, 2016

Math
40min * 1hr/60min * 69mi/hr * 1gal/23mi = 2 gal
July 10, 2016

Assembly language
so, what have you done so far?
July 10, 2016

Maths
Your answer is correct, but where did that 10 come from in the line above it?
July 10, 2016

Pre-Calculus 11
yes -∛54 = ∛-54 Did you try your answer for the other one?? (2/3)^2-5 is negative. so its square root is not real 3-x = √(x^2-5) 9-6x+x^2 = x^2-5 6x = 14 x = 7/3 Let's try 7/3 3 - 7/3 = 2/3 √(49/9-5) = √4/9 = 2/3 Check the graphs at http://www...
July 10, 2016

science
Since KE = 1/2 mv^2, you just plug in your numbers to get the energy in Joules: 1/2 * 70.0 * (1000m/10s)^2
July 10, 2016

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