Question

Найдите tga, если sina= -4/5, 180 ≤ а ≤ 270

Answer 1

$sina=-frac{4}{5}\\180^circ textless a textless 270^circ ; ; ; Rightarrow quad tga textgreater 0; ,; ; cosa textless 0\\cosa=-sqrt{1-sin^2a}=-sqrt{1- frac{16}{25} }=-sqrt{frac{9}{25}}=- frac{3}{5} \\tga=frac{sina}{cosa}= frac{-4/5}{-3/5} = frac{4}{3}$