Question

Sec2x = what?

Answer 1

Really having trouble with this one.. :/

Answer 2

Trig identities aren't my thing.

Answer 3

hope you know sec x = 1/cos x

so sec2x = 1/cos2x = 1/cos(x+x)

cos(x+x) = ?

use formula cos(a+b) = ---- ? hope you know it

Answer 4

Yes! Thank you.
cosacosb + sinasinb
Which would be:
2cosa + 2sina right?

Answer 5

2cosx + 2sinx I mean.

Answer 6

so there are in place of a and b just x and cosx *cosx = cos^2 x not 2cosx

ok. ?

Answer 7

Oh, right!

Answer 8

so in this case cos(x3x) = cosx*cosx +sinx*sinx = cos^2 x +sin^2 x

but you know this formula that this is equal how many from trigonometry formulas ?

Answer 9

sorry there wan being cos(x+x) = ---

Answer 10

Wait... there should be a minus sign, shouldn't there?
cos^2x - sin^2x

Answer 11

but than you check you wrote above plus not minus - yes ?

Answer 12

I know, but I looked up the formula and it says something different..

Answer 13

ok so than how is correct ? with minus ?

so than you get cos(x+x) = cos^2 x - sin^2 x =

using formula cos^2 x +sin^2 x = 1 => cos^2 x = 1 -sin^2 x so this substituted inside your equation in place of cos^2 x what will get ?

Answer 14

I think I got it... I was confused because I was thinking cos(a+b) = cosacosb + sinasinb, when it should have been cosacosb - sinasinb
I think I have it from here! Thank you for your help.

Answer 15

np

was my pleasure

good luck