Trigonometry 1

i) 8 sin^2 a - 9 cos^2 a = 6 sin a cos a

8sin^2 a - 6 sin a cos a - 9 cos^2 a = 0

( 4 sin a + 3 cos a )( 2 sin a - 3 cos a ) = 0

tan a = -3 / 4 or tan a = 3 / 2

ii) tan a = -3 / 4 has no solution in 0 <= a <= 180*

For tan a = 3 / 2,

a = 56.31* ( 2 d.p. )


2008-02-04 12:34:47 補充：
Sorry for a typing error:tan a = -3 / 4 has 1 solution in 0 &lt;= a &lt;= 180*a = 143.13* ( 2 d.p. )For tan a = 3 / 2, a = 56.31* ( 2 d.p. )

56.31* and 143.31*