Question

Rút gọn:
a. (1-cos)(1+cos)
b. tan^2 (2cos^2 +sin^2 -1)
c. sin^4 +cos^4 + 2cos^2 * sin^2

 

Answer 1

a: \(\left(1-cosx\right)\left(1+cosx\right)=1^2-cos^2x=sin^2x\)

b: \(tan^2x\left(2cos^2x+sin^2x-1\right)\)

\(=tan^2x\left(1-1+cos^2x\right)\)

\(=\dfrac{sin^2x}{cos^2x}\cdot cos^2x=sin^2x\)

c: \(sin^4x+cos^4x+2\cdot cos^2x\cdot sin^2x\)

\(=\left(sin^2x+cos^2x\right)^2\)

\(=1^2=1\)