giúp e chứng minh biểu thức k phụ thuộc vào x A=2sin^4(x) – sin^4(x) + sin^(x)cos^(x)+3sin^(x)

$A= $2\sin^4x-\sin^4x+\sin^2x.\cos^2x+3\sin^2x$

$= \sin^4x+\sin^2x\cos^2x+\sin^2x+2\sin^2x$

$= \sin^4x+\sin^2x(\cos^2x+1)+2\sin^2x$

$= \sin^4x+\sin^2x(2\cos^2x+\sin^2x)+2\sin^2x$

$= 2\sin^4x+2\sin^2x\cos^2x+2\sin^2x$

$= 2\sin^2x(\sin^2x+\cos^2x)+2\sin^2x$

$= 2\sin^2x+2\sin^2x$

$= 4\sin^2x$ (Không CM được).