3 years ago

3 Prove thatcos130°+cos 110+ cos10=0

Mathematics

1 answer:

Evgesh-ka [11]3 years ago

5 0

We know, cos A + cos B = 2cos(C+D)/2 × cos(C - D)/2

So,

cos 130 + cos 110 + cos 10

cos 130 + 2cos (110+10)/2 × cos( 110-10)/2

cos 130 + 2cos 60 × cos 50

cos ( 180 - 50 ) + 2cos60 cos 50

We know, cos ( 180 - A ) = -cos A

2cos 60 cos 50 - cos 50

Also, cos 60 = 0.5

2×0.5 cos 50 - cos50

cos 50 - cos 50

0 = RHS.

Hence proved

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3 Prove thatcos130°+cos 110+ cos10=0​

3 Prove thatcos130°+cos 110+ cos10=0