Mathematics

Which value of x solves the equation cos x° = sin (20° + x°), where 0 < x < 90?

$cosx^o=sin(20^o+x^o)\\\\--------------------\\\\cosx^o=sin(90^o-x^o)\ then:\\\\sin(90^o-x^o)=sin(20^o+x^o)\ and\ x^o\in(0^o;\ 90^o)\ iff\\\\90^o-x^o=20^o+x^o\\\\-x^o-x^o=20^o-90^o\\\\-2x^o=-70^o\ \ \ \ /:(-2)\\\\x^o=35^o$