sin(5x-9)=cos(10x-6)

sin (5x - 9)  = cos (10x - 6)

Note that, because they are co-functions,    (5x - 9) + (10 x - 6)  = 90      simplify

15x - 15  =  90     add 15 to both sides

15x  = 105    divide both sides by  15

x = 7