Question

if sin(3x+10)degrees = cos20degrees, find x

Answer 1

http://ichthyosapiens.com/School/Math/Trig/ch05CofunctionIdentities.jpg <--- notice those

Answer 2

Therefore, the cos(20) = sin(70). Do you see the connection? Solve for x.

Answer 3

\(\bf {\color{blue}{ sin(90^o-\square^o )=cos(\square^o )}}
\\ \quad \\ \quad \\
sin[(3x-10)^o]=cos(20^o)\implies sin[(3x-10)^o]={\color{blue}{ sin(90^o-20^o)}}
\\ \quad \\
sin[(3x-10)^o]={\color{blue}{ sin(70^o)}}\implies 3x-10=70\)