Question

1/cos2a - 1=tg2a
Помните

Answer 1

$frac{1}{cos^2a}-1=frac{1-cos^2a}{cos^2a}=frac{sin^2a}{cos^2a}=tg^2a\\\star ; ; sin^2a+cos^2a=1; ; Rightarrow ; ; sin^2a=1-cos^2a; ; star \\star ; ; frac{sina}{cosa}=tga; ; star quad Rightarrow \\star ; ; 1+tg^2a=frac{1}{cos^2a}; ; star$