Because sina=4/5, A is the second quadrant angle.

So cosa=-3/5

So: sin2a=2sinacosa

=2x4/5x(-3/5)

=-24/25

cos2a= 1-2sin？ a

= 1-2x(4/5)？

=-7/25

tan2a=sin2a/cos2a

=-24/25/-7/25

=24/7

See the picture for the answer to question 5?

See the picture for the answer to question 6?

Question 8 proves that:

The left side of the equation

=(cos？ a)？ -(sin? a)？

=(cos？ A+ sin? a)(cos？ Sin. answer

= 1xcos2a

=cos2a

= Right side of the equation

(license)

Question 9. See the picture?