If cos ( x ) = 9 10 (in Quadrant-I), find the following. sin ( 2 x ) =?

Answer 1

sin(2x) = 2sinxcosx; sinx = √(1 - 81/100) = √19/10.

So, sin(2x) = 2·(9/10)·(√19/10) = 9√19/50