Respuesta :

chi3fcomm5nd
you need to use the identity
cos(90-u)=sin(u)
if u=x-20
cos(90-x+20)=sin(x-20)
cos(110-x)=sin(x-20)
substituting in the original function
cos(110-x)=cos(42)
for the functions to be equal there input must be equal
110-x=42
x=68