cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)

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cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)cos(a-55)*cos(a+5)+sin(a-5

cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)
cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)

cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)
cos(a-55)*cos(a+5)+sin(a-55)*sin(a-5)
=cos[(a-55)﹣(a+5)]
=cos(-60)º
=1/2