Question

Find value of cos 210 wihout calculator with working

Answer 1

Answer:

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Step-by-step explanation:

cos (210°) = cos (180° + 30°)

since 180° is added with 30°

it will be in third quadrant

And, in 3rd quadrant cos is negative

cos( 180° + 30° ) = - cos (30°) = -(√3 / 2)

cos(210°) = -(√3/2)

Answer 2

Answer with explanation:

2cos 90°+ cos 30° = cos 210°

2× 0 + _/3/2 = cos 210°

cos210°= _/3/2