Jawapan

2016-06-17T20:18:49+08:00

cos 2x= 1-2sin²x

3(1-2sin²x)-8sinx+5=0

-6sin²x-8sinx-8=0

6sin²x+8sinx-8=0

3sin²x+4sinx-4=0

(3sinx-2)(sinx+2)=0

sinx= 2/3            sinx=-2 (rejected)

x=41.81, 138.19