F4 Maths

樓上好似有啲錯...

應該 First change all angle to reference angle:

= tan^2 30度-sin^2(100度)-cos^2 100度
(因全部有2次方,所以不用考慮正負號)

= tan^2 30度-(sin^2(100度)+cos^2 100度)
= tan^2 30度-1
= (1/sqroot(3))^2 - 1
= 1/3 - 1
= -2/3

(-tan30)^2-(-sin 80)^2-(-cos 80)^2=-2/3
1/3 - ( sin^2 80+cos^2 80)
1/3 -1
-2/3

2012-04-28 11:01:55 補充：
樓下:
-sin 80=sin(-100)
cos 460=cos100=-cos80