15-05-2016
Mathematics

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sin78 ×cos42+cos78×sin42 evaluate without the use of a calculator

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15-05-2016

sin a * cos b + cos a * sin b=sin (a+b)

sin 78 * cos 42 + cos 78* sin 42=sin (78+42)=sin 120=sin(180-120)=
sin 60=√3 / 2

Answer: sin 78 * cos 42 + cos 78* sin 42=√3 / 2

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