2. Prove that sin 750° cos 480° + cos 120° cos 60° = _1÷2
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Answer:
sin750degree.cos480degree+cos120degree.cos60degree
= sin(720 + 30) cos (360 + 120) + cos (180 - 60) cos 60
= sin 30 cos 120 - cos 60 cos 60
= sin 30 cos (180 - 60) - cos^2 60
= -sin30 cos 60 - cos^2 60
= -(1/2)(1/2) - (1/2)^2
= -1/4 - 1/4
= -2/4
= -1/2
Step-by-step explanation:
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