Question

[Biện Bạch Ngọc]

1/ Cho \(\sin\alpha=0,28.\)Tính \(\cos\alpha\), tg\(\alpha\), cotg\(\alpha\)

2/ Cho góc nhọn \(\alpha\). chứng minh rằng: \(1-2\cos^2\alpha=\sin^4\alpha-\cos^4\alpha\)

Answer 1

[Nguyễn Lê Phước Thịnh]

Câu 1: 

\(\cos a=\sqrt{1-0.28^2}=\dfrac{24}{25}\)

\(\tan a=\dfrac{0.28}{0.96}=\dfrac{7}{24}\)

\(\cot a=\dfrac{1}{\tan a}=\dfrac{24}{7}\)