Tính:
a, sin x. cos x
b, sin^2 x – cos^2 x
c, sin^2 x – 1
d, (sin x + cos x)^2
Tính: a, sin x. cos x b, sin^2 x – cos^2 x c, sin^2 x – 1 d, (sin x + cos x)^2
By Alexandra
By Alexandra
Tính:
a, sin x. cos x
b, sin^2 x – cos^2 x
c, sin^2 x – 1
d, (sin x + cos x)^2
a. $sinx.cosx=\frac{1}{2}sin2x$
b. $sin^2x-cos^2x=(sinx-cosx)(sinx+cosx)$
c. $sin^2x-1=sin^2x-cos^2x-sin^2x=-cos^2x$
d. $(sinx+cosx)^2=sin^2x+2sinx.cosx+cos^2x$
$=1+sin2x$
a, $sinx.cosx= \frac{1}{2}sin2x$
b, $sin^2x-cos^2x= (sinx+cosx)(sinx+cosx)$
c, $sin^2x-1= -cos^2x$
d, $(sinx+cosx)^2= sin^2x+2sinxcosx+cos^2x= 1+sin2x$