using the trigonometric identities
tanx = [tex]\frac{sinx}{cosx}[/tex] and sin²x = 1 - cos²x
3sinxtanx = 8
( 3sin²x)/ cosx = 8 ( multiply both sides by cosx )
3( 1 - cos²x ) = 8cosx
3 - 3cos² = 8cosx ( subtract 3 - 3cos²x from both sides )
0 = 3cos²x + 8cosx - 3
