Phương trình lương giác lớp 11 khó

Q

quynhsieunhan

1, $32cos^6x - cos6c = 1$
\Leftrightarrow $32(\frac{1 + cos2x}{2})^3 - 4cos^32x + 3cos2x = 1$
\Leftrightarrow $4(cos^32x + 3cos^22x + 3cos2x + 1) - 4cos^32x + 3cos2x = 1$
\Leftrightarrow $12cos^32x + 15cos2x + 3 = 0$
\Leftrightarrow $cos2x = -1$ hoặc $cos2x = \frac{-1}{4}$
 
You must log in or register to reply here.
Top Bottom