Question

Tính sina và tana:

a) cosa = \(\dfrac{5}{13}\)

b) cosa = \(\dfrac{15}{17}\)

c) cosa = 0,6

(Không dùng Py ta go)

Answer 1

a) Áp dụng hệ thức:

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

<=>\(sin^2\alpha+\left(\dfrac{5}{13}\right)^2=1\)

<=>\(sin^2\alpha+\dfrac{25}{169}=1\)

<=>\(sin^2\alpha=1-\dfrac{25}{169}=\dfrac{144}{169}\)

<=>\(sin\alpha=\sqrt{\dfrac{144}{169}}=\dfrac{12}{13}\)

Ta có: \(tan\alpha=\dfrac{sin\alpha}{cos\alpha}=\dfrac{\dfrac{12}{13}}{\dfrac{5}{13}}=\dfrac{12}{13}.\dfrac{13}{5}=\dfrac{12}{5}\)