Cách làm cho bạn:
a) 1 + $tan^{2}$$\alpha $
= 1 + $(\frac{sin\alpha}{cos\alpha})^{2}$
= $\frac{cos^{2}\alpha + sin^{2}\alpha}{cos^{2}\alpha}$
= $\frac{1}{cos^{2}\alpha}$.
b) 1 + $cot^{2}$$\alpha $
= 1 + $(\frac{cos\alpha}{sin\alpha})^{2}$
= $\frac{cos^{2}\alpha + sin^{2}\alpha}{sin^{2}\alpha}$
= $\frac{1}{sin^{2}\alpha}$
c) $tan^{2}$$\alpha $(2$sin^{2}$$\alpha $ + 3$cos^{2}$$\alpha $ - 2)
= $tan^{2}$$\alpha $($cos^{2}$$\alpha $ + 2($sin^{2}$$\alpha $ + $cos^{2}$$\alpha $) - 2)
= $\frac{sin^{2}\alpha}{cos^{2}\alpha}$x$cos^{2}$$\alpha $ = $sin^{2}$$\alpha $.
Bình luận