Question

integrate Cos(3x)Cos(2x)...any help?

Answer 1

I think we treat 3x as alpha and 2x as beta, so it's like Integrate Cos(a)cos(b)

Answer 2

Maybe I need to use some sort of trig formula?

Answer 3

\[\cos(u)\cos(v)=\frac12\big[\cos(u-v)+\cos(u+v)\big]\]

Answer 4

hi...can you possibly explain this procedure to me a little?

Answer 5

How did you get that formula?

Answer 6

I've just copied one of the Product and Sum Formulas, I can never remember these formulas but I know where to find them .

Answer 7

It looks like a trig identity but I can't find it in my book or what it would be called

Answer 8

it's called a sum and product formula?

Answer 9

what you should do is let
3x=alpha=u
3x=beta=v

Answer 10

Yeah under trig formulas- sum and product formulas

Answer 11

so I am doing Integration by Parts on this?

Answer 12

you dont need to do integration by parts for this problem if you use the tri formula

Answer 13

oh...I see...I got confused because of the u and v

Answer 14

quick question...

Answer 15

is this a sum formula? sin(a+b) = sinacosb+cosasinb

Answer 16

\[\int \cos(3x)\cos(2x)\mathrm dx\]\[=\frac12\int \cos(3x-2x)+\cos(3x+2x)\mathrm dx\]\[=\]

Answer 17

i think that \(\sin(a+b) = \sin a\cos b+\cos a\sin b \)
is called an angle sum formula

Answer 18

ok...I think i can integrate it from where you left off...my dumb book totally doesn't have those listed in there though...geesh...but thank you!

Answer 19

so final answer is 1/2sinx + 1/10sin(5x) +c ?

Answer 20

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