The exact value of cos120 if the measure 120 degrees intersects the unit circle at point (-1/2,√3/2) is 0.5
Solving trigonometry identity
If an angle of measure 120 degrees intersects the unit circle at point (-1/2,√3/2), the measure of cos(120) can be expressed as;
Cos120 = cos(90 + 30)
Using the cosine rule of addition
cos(90 + 30) = cos90cos30 - sin90sin30
cos(90 + 30) = 0(√3/2) - 1(0.5)
cos(90 + 30) = 0 - 0.5
cos(90 + 30) = 0.5
Hence the exact value of cos120 if the measure 120 degrees intersects the unit circle at point (-1/2,√3/2) is 0.5
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