Show that: cos 2 θ cos θ/2 − cos 3 ...
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Check here step-by-step solution of 'Show that: cos 2 θ cos θ/2 − cos 3 θ cos 9θ/2 = sin 5 θ sin 5θ/2' question at Instasolv!
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Show that: ( cos 2 theta cos frac{theta}{2}-cos 3 theta cos frac{9 theta}{2}=sin 5 theta sin frac{5 theta}{2} )

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Show that: cos 2 θ cos θ/2 − cos 3 θ cos 9θ/2 = sin 5 θ sin 5θ/2
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( 2 cos 2 theta cos frac{theta}{2}-cos 3 theta cos frac{9 theta}{2}=frac{-cos frac{3 theta}{2}+cos frac{50}{2}-cos frac{150}{2}+cos 3 theta}{2} )
( =frac{cos frac{50}{2}-cos frac{150}{2}}{2}=frac{2}{2} sin left(frac{150-frac{50}{2}}{2}right) sin left(frac{150+frac{50}{2}}{2}right) )
( =sin left(frac{10 theta}{4}right) sin left(frac{20 theta}{4}right)=sin (5 theta) sin left(frac{5 theta}{2}right) )

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