trig
Reduce the following to the sine or cosine of one angle:
(i) sin145*cos75  cos145*sin75
(ii) cos35*cos15  sin35*sin15
Use the formulae:
sin(a+b)= sin(a) cos(b) + cos(a)sin(b)
and
cos(a+b)= cos(a)cos(b)  sin(a)sin)(b)
(1)The quantity = sin(14575)
= sin 70
= cos 20
note that If a+b=90 degrees then
sin a = cos b
(2) The quantity = cos (35 + 15)
= cos 50
= sin 40
asked by
Paul C
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