Question

1-2cos^2 13°/cos26°
как решить?

Answer 1

$frac{1-2* cos^{2} 13^{0} }{cos 26^{0} } = frac{-(2* cos^{2} 13^{0} -1 )}{cos 26^{0} } = frac{-cos(2* 13^{0} )}{cos 26^{0} } = frac{-1*cos 26^{0} }{cos 26^{0} }=-1$