${(\cos \alpha + \cos \beta )^2} + {(\sin \alpha + \sin \beta )^2} = $
${(\cos \alpha + \cos \beta )^2} + {(\sin \alpha + \sin \beta )^2} = $
- A
$4{\cos ^2}\frac{{\alpha - \beta }}{2}$
- B
$4{\sin ^2}\frac{{\alpha - \beta }}{2}$
- C
$4{\cos ^2}\frac{{\alpha + \beta }}{2}$
- D
$4{\sin ^2}\frac{{\alpha + \beta }}{2}$
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The value of $\sum_{r-1}^{18} cos^2(5r)^o,$ where $x^o $ denotes the $x$ degree, is equals to
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