10. If sin 0 + sin d = a and cos 0 ...
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10. If sin 0 + sin d = a and cos 0 + cos 0 = b, then (B) cos ') = + va? –b? (A) cos () + 1 Va? +6° (C) tan(-4) = / a> +6²-2 (D) cos (0 - 0) =

JEE/Engineering Exams
Maths
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( sin theta+sin phi=a ) ( Rightarrow 2 sin frac{theta+phi}{2} cos frac{theta+theta}{2}=a cdot 0 ) and ( cos theta+cos phi=b ) ( Rightarrow 2 cos frac{theta+phi}{2} cos frac{theta-phi}{2}=b quad(2) ) ( frac{0^{2}+0}{4 cos ^{2} theta-phileft(sin ^{2} frac{theta+phi}{2}+cos ^{2} frac{theta+phi^{2}}{2}right)=a^{2}+b^{2}} ) ( Rightarrow quad 4 cos frac{theta-phi}{2}=a^{2}+b^{2} ) ( Rightarrow quad cos ^{2} frac{theta-phi}{2}=frac{a^{2}+b^{2}}{4} ) ( Rightarrow quad cos frac{theta-phi}{2}=pm frac{1}{2} sqrt{a^{2}+b^{2}} )
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