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=(cos^2(65)-sin^2(65) ) / ( 7 sin(40)/2 ) =
=(cos(130) ) / ( 7 sin(40)/2 ) =
=2(cos(90+40) ) / ( 7 sin(40) ) =
= - 2(sin(40) ) / ( 7 sin(40) ) =
= - 2 / 7