Question

15cosx+27 sin^2 x+27cos^2 x=26​

Answer 1

$15cosx+27(sin^2x+cos^2x)=26\\15cosx+27*1=26\\15cosx=26-27\\15cosx=-1\\cosx=-\frac{1}{15} \\x=\pm(\pi -arccos(\frac{1}{15}))+2\pi  k, k \in Z$