Question 934032
If cos(A) = -5/13, where pi/2 is less than or equal to A < pi, then evaluate cos(A-(pi/4))
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sin(A)=12/13 (working with a (5-12-13) reference right triangle in quadrant II)
reference angle A is in quadrant II
cos(x-y)=cosxcosy+sinxsiny
cos(A-(&#960;/4))=cosAcos(&#960;/4)+sinAsin(&#960;/4)
=-5/13*(&#8730;2/2)+12/13*&#8730;2/2
=-5&#8730;2/26+12&#8730;2/26=7&#8730;2/26
cos(A-(pi/4))=7&#8730;2/26