Question

tgA =4
Найдите. ctgA, sinA, cosA?

Answer 1

$tga=4\\ctga=frac{1}{tga}=frac{1}{4}\\1+tg^2a=frac{1}{cos^2a}; ; to ; ; ; 1+16=frac{1}{cos^2a}; ; ,; ; frac{1}{cos^2a}=17; ; to ; ; cos^2a=frac{1}{17}; ,\\cosa=pm frac{1}{sqrt{17}}=pm frac{sqrt{17}}{17}\\sina=pm sqrt{1-cos^2a}=pm sqrt{1-frac{1}{17}}=pm sqrt{frac{16}{17}}=pm frac{4}{sqrt{17}}=pm frac{4sqrt{17}}{17}$