Question

giúp vs

Answer 1

a: cosx=cos15 độ

=>\(\left[{}\begin{matrix}x=15^0+k\cdot360^0\\x=-15^0+k\cdot360^0\end{matrix}\right.\)

b: \(cos2x=cos\left(x+60^0\right)\)

=>\(\left[{}\begin{matrix}2x=x+60^0+k\cdot360^0\\2x=-x-60^0+k\cdot360^0\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}2x-x=60^0+k\cdot360^0\\2x+x=-60^0+k\cdot360^0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=60^0+k\cdot360^0\\x=-20^0+k\cdot120^0\end{matrix}\right.\)