Find the value of Cos 225°
1. 0.7071
2. -0.866
3. 0.866
4. -0.7071
1. 0.7071
2. -0.866
3. 0.866
4. -0.7071
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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