Question

Вычислите (tg a+ctg a)*cos a, если sin a=0,4

Answer 1

$(tg(a)+ctg(a))*cos(a)=sin(a)+ \frac{ cos^{2}(a) }{sin(a)}=sin(a)+ \frac{1- sin^{2}(a) }{sin}= \\ = \frac{ sin^{2}(a)+1- sin^{2}(a) }{sin(a)}= \frac{1}{sin(a)}=1/0.4=10/4=2.5$