Question

prove that cos 105 + cos 15=sin 75-sin 15

Answer 1

LHS =cos105 + cos15
=cos (90+15) + cos (90-75)
=-sin15+sin75
=sin75-sin15=RHS

Answer 2

Answer:

cos105°+cos15° = sin75°-sin155°

Step-by-step explanation:

LHS = cos105° +cos15°

=cos(90°+15°)+cos(90°-75°)

/* We know that,

i ) cos(90°+A) = -sinA

ii) cos(90°-A) = SinA

= -sin15°+sin75°

=sin75°-sin15°

=RHS

Therefore,

cos105°+cos15° = sin75°-sin155°

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