If A and B are supplementary, then find the value of cosA cosB – sinA sinB.

If A and B are supplementary, then find the value of cosA cosB – sinA sinB. Correct Answer -1

Given:

A and B are supplementary i.e. A + B = 180°.

Formula Used:

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cos(A + B) = cosA cosB – sinA sinB

Calculation:

cosA cosB – sinA sinB

⇒ cos(A + B)

⇒ cos180°

⇒ cos(90° + 90°)

⇒ -sin 90°

⇒ -1