Question

Use an identity to find the value of

Answer 1

`\bigodot\: - \sin\theta.`

Explanation:

• We know that:
• cos (A + B) = cos A . cos B - sin A . sin B

• 
  `\implies \cos (\theta +90\degree) =\cos\theta.\cos 90\degree - \sin\theta.\sin 90\degree`

• 
  `\implies \cos (\theta +90\degree) =\cos\theta.0 - \sin\theta.1`

• 
  `\implies \cos (\theta +90\degree) =0 - \sin\theta.`

• 
  `\implies \cos (\theta +90\degree) = - \sin\theta.`