Question

cos(alpha+beta)cos(alpha-beta)= ......
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Answer 1

cos(alpha + beta)*cos(alpha - beta)

=> cos^2[(alpha + beta)(alpha - beta)]

=> cos^2(alpha^2 - alpha^2)

Hope it helps you.

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Answer 2

$<font color=green>$

$\underline\red{Given}$ :-

Cos ( $\alpha$ + $\beta$ . Cos $\alpha$ - $\beta$

$\underline\red{Solution}$ :-

Use $\bf\blue{formula}$

• Cos (A + B) = Cos A Cos B - Sin A Sin B
• Cos (A - B) = Cos A Cos B + Sin A Sin B

Cos $\alpha$ + $\beta$ - Cos $\alpha$ - $\beta$

→ Cos $\alpha$ Cos $\beta$ - Sin $\alpha$ Sin $\beta$ - ( Cos $\alpha$ Cos $\beta$ + Sin $\alpha$ Sin $\beta$ )

→ Cos $\alpha$ Cos $\beta$ - Sin $\alpha$ Sin $\beta$ - Cos $\alpha$ Cos $\beta$ - Sin $\alpha$ Sin $\beta$

→ -2Sin $\alpha$ Sin $\beta$

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