中四數學一條,關於三角學! 急!!

x^2 + 3x sin@ - cos^2 @ = 0 , ( 0 < @ < 360 )

the sum of the squares of the two roots
= a^2 + b^2 = (a^2 + 2ab + b^2 - 2ab) = (a + b)^2 - 2ab = 11/2......*
Sum of the roots = a + b = - 3sin@
Product of the roots = ab = - cos^2 @
Sub to * :
(- 3sin@)^2 - 2( - cos^2 @) = 11/2
9(sin@)^2 + 2(cos@)^2 = 11/2
7(sin@)^2 + 2(sin@)^2 + 2(cos@)^2 = 11/2
7(sin@)^2 + 2[(sin@)^2 + 2(cos@)^2] = 11/2
7(sin@)^2 + 2(1) = 11/2
7(sin@)^2 = 11/2 - 4/2 = 7/2
(sin@)^2 = 1/2