Question

Answer 1

a: \(\sin^2\left(x+k\pi\right)=\left(-1\right)^{2k}\cdot\sin^2x=\sin^2x\)

=>\(-\sin^2x=-\sin^2\left(x+k\pi\right)\)

=>\(f\left(x\right)=f\left(x+k\pi\right)\)

=>ĐPCM

b:TXĐ là D=R\{\(\frac{\pi}{2}+k\pi\) }

\(\tan^2\left(x+k\pi\right)=\tan^2x\)

=>\(3\cdot\tan^2x=3\cdot\tan^2\left(x+k\pi\right)\)

=>\(3\cdot\tan^2x+1=3\cdot\tan^2\left(x+k\pi\right)+1\)

=>\(f\left(x\right)=f\left(x+k\pi\right)\)

=>ĐPCM

c: \(y=\sin x\cdot cosx=\frac12\cdot\sin2x\)

\(f\left(x+k\pi\right)=\frac12\cdot\sin\left\lbrack2\left(x+k\pi\right)\right\rbrack\)

\(=\frac12\cdot\sin\left\lbrack2x+2k\pi\right\rbrack=\frac12\cdot\sin2x\)

=f(x)

=>ĐPCM