SOLUTION: Find the exact value of the expression. Cos 93 cos87-sin93 sin87

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Question 1012845: Find the exact value of the expression. Cos 93 cos87-sin93 sin87
Answer by anand429(138) About Me  (Show Source):
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Cos 93 cos87-sin93 sin87
=Cos(90+3)*cos(90-3)-sin(90+3)*sin(90-3)
=(cos90*cos3-sin90*sin3)*(cos90*cos3+sin90*sin3) - (sin90*cos3-cos90*sin3)*(sin90*cos3+cos90*sin3)
= ((cos90*cos3)^2-(sin90*sin3)^2) - ((sin90*cos3)^2-(cos90*sin3)^2)
= 0 -(sin3)^2 -(cos3)^2 -0
= -1