Question

If tanx=-4/3 and x is in quadrant 2 then cos2x=? A. 7/25 b. -3/5 c. -7/25 d. 3/5

Answer 1

= (1 - tan^2 (x)) / (1 + tan^2 (x))  

= (1 - (-4/3)^2) / (1 + (-4/3)^2)  

= (1 - (16/9)) / (1 + (16/9))  

= (9 - 16) / (9 + 16) [By multiplying numerator and denominator with 9]  

= (-7) / (25)  

= -7/25