Question

If sin theta=3/5 and theta is in quad 2 the exact form of cos (2theta) is
I just need my work to be checked! because I got postive or neg sqrt -1/2

Answer 1

cos (2theta0 = 1 - 2sin^2 theta

Answer 2

Yeah I got that far knowing which formula to use

Answer 3

so 1-2*(3/5)^2

Answer 4

= 1 - 2*9/25

Answer 5

Wait how tho?

Answer 6

Thats not what I got at all lol

Answer 7

7/25

Answer 8

yes

Answer 9

But how? It doesnt make sense lol @welshfella

Answer 10

I'm assuming you mean 'cos 2 theta' not 'cos theta squared'?

Answer 11

Yes exactly. Is it that simple then? Haha I was solving for sin @welshfella

Answer 12

I do mean cos2theta

Answer 13

yes - you just substitute 3/5 for sin theta

Answer 14

Ohhhh I see @welshfella