Question

ctga+1/ctga-1  если sina=7/25 и    пи/2 меньше a меньше пи

Answer 1

$sin alpha =frac{7}{25},; ; frac{pi}{2}< alpha <pi ; ,; ; to ; ; cos alpha <0\\cos alpha =-sqrt{1-sin^2 alpha }=-sqrt{1-frac{49}{625}}=-sqrt{frac{576}{625}}=-frac{24}{25}\\\frac{ctg alpha +1}{ctg alpha -1}=frac{frac{cos alpha }{sin alpha }+1}{frac{cos alpha }{sin alpha }-1}=frac{cos alpha +sin alpha }{cos alpha -sin alpha }=frac{-frac{24}{25}+frac{7}{25}}{-frac{24}{25}-frac{7}{25}}=frac{17}{31}$

Answer 2

спасибо