f.2 Trigonometric

29.
sin21 - cos69
=cos(90-21)-cos69
=cos69-cos69
=0

31
cos78/tan12 - sin78
=sin12x(cos12/sin12) - sin78
=cos12 - cos12
=0

33
tan(90-x)
1 - cos^2(90-x)
= 1/tanx
1 - sin^2(x)
=cosx/sinx
cos^2(x)
=1/sinxcosx

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29
sin21 - cos69 = cos69 - cos69
= 0
31
(cos78)/(tan12) -sin78 = (cos78)(tan78) - sin78
= 0
33 [tan(90-theta)]/1-cos^(2)(90-theta)
= [tan(90-theta)] / sin^(2)(90-theta)
=1/[sin(90-theta)cos(90-theta)]

2012-05-20 19:25:24 補充：
恩,q33漏左個step
=1/[sin(90-theta)cos(90-theta)]
=1/cos(theta)sin(theta)