c)đặt$ A=cosx\times cos2x\times cos4x\times cos8x=\frac{1}{16}$$\Rightarrow \frac{1}{16}sinxsin2xsin4xsin8x=\frac{1}{16}sin2xsin4xsin8xsin16x$$\Rightarrow sinx=sin16x$
c)đặt$ A=cosx\times cos2x\times cos4x\times cos8x=\frac{1}{16}$$2A=sin2x\times cos 2x\times cos4x \times 8x=\frac{1}{8}$tương tự như thế cuối cùng ta có $16A=sin16x=1$$\Rightarrow 16x=\frac{\pi }{2}+2k\pi $$\Rightarrow x=\frac{\pi }{32}+\frac{\pi }{8}$
c)đặt$ A=cosx\times cos2x\times cos4x\times cos8x=\frac{1}{16}$$\
Ri
ght
arro
w \frac{1}{
16}
sin
xsin
2xsin
4x
si
n8x=\frac{
1}{
16}
sin2
xsin4xsin8xsi
n16x$$\Rightarrow
sinx=
si
n16x$