Ta có : pt $\Leftrightarrow \sin^4 x+\cos^{15} x=\sin^2 x+\cos^2 x$$\Leftrightarrow \sin^2 x(\sin^2 x-1)= \cos^2 x(1-\cos^{13} x) vì VT\geq 0\geq VP suy ra VT=VP=0$ :)
Ta có : pt \Leftrightarrow \sin^4 x+\cos^{15} x=\sin^2 x+\cos^2 x\Leftrightarrow \sin^2 x(\sin^2 x-1)= \cos^2 x(1-\cos^{13} x) vì VT\geq 0\geq VP suy ra VT=VP=0 :)
Ta có : pt $\Leftrightarrow \sin^4 x+\cos^{15} x=\sin^2 x+\cos^2 x
$$\Leftrightarrow \sin^2 x(\sin^2 x-1)= \cos^2 x(1-\cos^{13} x)
vì VT\geq 0\geq VP
suy ra VT=VP=0$ :)