Question

[Linh]

Đơn giản các biểu thức sau:

(1-\(Cos\alpha\)).\(\left(1+Cos\alpha\right)\)

\(1+sin^2\alpha+cos^2\alpha\)

\(sin^4\alpha+cos^4\alpha+2sin^2\alpha.cos^2\alpha\)

\(tan^2\alpha-sin^2\alpha.tan^2\alpha\)

\(cos^2\alpha+tan^2\alpha.cos^2\alpha\)

\(tan^2\alpha.\left(2cos^2\alpha+sin^2\alpha-1\right)\)

Gấp!!!:))))

Answer 1

[Yuzu]

\(\left(1-\cos\alpha\right)\left(1+\cos\alpha\right)=1-\cos^2\alpha=\left(\sin^2\alpha+\cos^2\alpha\right)-\cos^2\alpha\\ =\sin^2\alpha\)

\(1+\sin^2\alpha+\cos^2\alpha=1+1=2\)

\(\sin^4\alpha+\cos^4\alpha+2\sin^2\alpha\cdot\cos^2\alpha\\ =\left(\sin^2\alpha\right)^2+2\sin^2\alpha\cdot\cos^2\alpha+\left(\cos^2\alpha\right)^2\\ =\left(\sin^2\alpha+\cos^2\alpha\right)^2\\ =1^2=1\)

Answer 2

[Yuzu]

\(\tan^2\alpha-\sin^2\alpha\cdot\tan^2\alpha\\ =\tan^2\alpha\left(1-\sin^2\alpha\right)\\ =\left(\frac{\sin\alpha}{\cos\alpha}\right)^2\cdot\cos^2\alpha\\ =\frac{\sin^2\alpha}{\cos^2\alpha}\cdot\cos^2\alpha\\ =\sin^2\alpha\)

\(\cos^2\alpha+\tan^2\alpha\cdot\cos^2\alpha\\ =\cos^2\alpha+\left(\frac{\sin\alpha}{\cos\alpha}\right)^2\cdot\cos^2\alpha\\ =\cos^2\alpha+\frac{\sin^2\alpha}{\cos^2\alpha}\cdot\cos^2\alpha\\ =\cos^2\alpha+\sin^2\alpha\\ =1\)

\(\tan^2\alpha\cdot\left(2\cos^2\alpha+\sin^2\alpha-1\right)\\ =\tan^2\alpha\cdot\left(2\cos^2\alpha+\sin^2\alpha-\sin^2\alpha-\cos^2\alpha\right)\\ =\tan^2\alpha\cdot\cos^2\alpha\\ =\frac{\sin^2\alpha}{\cos^2\alpha}\cdot\cos^2\alpha=\sin^2\alpha\)