Question

i need an answer check!

Answer 1

the problem was \[\cos2\theta, when \sin \theta=-7/25 and \theta is \in Q3\] so cos2theta would be 527/625 right?

Answer 2

cos^2+sin^2 = 1

cos^2 = 1-sin^2

cos = sqrt(1-sin^2) ; and in q3 thats gonna be negative

Answer 3

but my teacher told us to use the double identity like cos 2A=1-2sin^2 ?

Answer 4

i misread it then, it bites getting old :)

Answer 5

cos(a+a) = cosacosa-sinasina = cos^2(a) - sin^2(a)

and thats where youd prolly use what i said at the start

Answer 6

cos^2 = 1-sin^2

cos^2-sin^2 = 1-sin^2 -sin^2 = 1-2sin^2

Answer 7

1- 98/25^2 = (25^2-98)/25^2

Answer 8

ok i see how u did it, that make a lot of sense thanks!

Answer 9

yw