1.

Find the value of Cos 225° 1. 0.70712. -0.8663. 0.8664. -0.7071

Answer» Correct Answer - Option 4 : -0.7071

Given:

Cos 225°

Formula Used:

Cos (180° + θ ) = -Cos θ

Concept Used:

Cosθ  in the third quadrant gives negative value.

Cos 45° = 1/√2

√2 = 1.414

Calculation: 

Cos 225° = Cos (180° + 45° )

⇒ Cos 225° = -Cos 45°

⇒ -Cos 45° = -1/√2 = 1000/1414 = -0.7071

The value of Cos 225° is -1/√2 or -0.7071



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