Solve sin2x + 4sin x + 3 = 0
sin² x + 4 sin x + 3 = 0Substitution: u = sin xu² + 4 u + 3 = 0u² + 3 u + u + 3 = 0u ( u + 3 ) + ( u + 3 ) = 0( u + 3 ) ( u + 1 ) = 0u = - 3, u = - 1;sin x = - 3 ( false )sin x = - 1Answer:x = 3 π / 2 + 2 k π , k ∈ Z
