Posted by **Sean** on Friday, March 14, 2008 at 9:00pm.

I know I've probably flooded the site or something (Sorry if I have), it's just that these problems aren't similar to anything I've reviewed in class. I've got two more questions, then maybe 1 or 2 more coming. That's all I can see in the future, anyhow.

1) Integral of [2* sqrt((1+cosx)/2)].

All I can see is that I take the 2 out of the integral, and put it out front.

2) Integral of [(sec(x))^4].

Here I'm completely stumped. I'm not sure how to start, either.

I'd really appreciate help on these two problems. They've really got me stuck.

P.S. Also, if anyone could supply a link of math tutorials of some sort, please do!

- Calculus - Integrals -
**Count Iblis**, Friday, March 14, 2008 at 11:11pm
1) use the formula:

cos(2x) = 2 cos^2(x) - 1

You can use this formula to derive a formula for cos(1/2 x) in terms of

cos(x). You can then simplify the square root using that formula.

2) sec^4 (x) = 1/cos^4(x)

You can use a reduction formula, which is easier to derive for positive powers of cos,, you just apply that backwards for this case.

Notation cos = c, sin = s:

c^n = c^(n-2)c^2 = c^(n-2)[1-s^2] =

c^(n-2) - c^(n-2)s^2

So the integral of c^n is the integral of c^(n-2) minus the integral of

c^(n-2)s^2. This latter integral can be written up to a minus sign:

Int of c^(n-2)sdc = ( let's do a partial integration) =

Integral of s d[c^(n-1)/(n-1)] =

Integral of d[sc^(n-1)/(n-1)] -

Integral of c^(n-1)/(n-1)ds =

sc^(n-1)/(n-1) -

Integral of c^(n)/(n-1) dx

So, we have expressed the integral of cos^n in terms of the integral of

cos^(n-2), a trignometric function and cos^n again. You can bring that later integral of cos^n back to the other side of this expression and solve for the integral of cos^n in terms of the integral of cos^(n-2).

You can then verify that this equation is also valid for negative n (that's is trivial). So, you can use it to express the integral of 1/c^4 in terms of the integral of 1/c^2, that latter integral is of course, the tan function.

- Calculus - Integrals -
**Sean**, Saturday, March 15, 2008 at 8:20am
I don't quite get how you did the first one. Mainly the cos(1/2 x)

## Answer this Question

## Related Questions

- calculus help - Is there any good calculus websites out there that teach every ...
- Tan^2 Integrals - I'm having a hard time understanding how to do Integrals ...
- eng 3-4 - i need the chapter reveiw questions for the story Two Friends in ...
- CALCULUS 2!!! PLEASE HELP!! - I'm having trouble with this question on arc ...
- MATH 2B Calculus - Consider the area between the graphs x+4y=14 and x+7=y^2. ...
- Calculus - I have two questions, because I'm preparing for a math test on monday...
- CALCULUS - what is the derivative of ln(x-1)? If you are studying the calculus ...
- Calculus (Partial Fractions) - My Calculus class just started Partial Fractions...
- Languages - what does .oot derob m'Iž mean? I have no idea what language this is...
- calculus - I'm having trouble with these two problems. If someone can help me ...