Question 1155615
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cos(theta)=5/13 in quadrant IV --> sin(theta) = -12/13.<br>
tan(psi) = -sqrt(3) in quadrant II --> sin(psi) = sqrt(3)/2, cos(psi) = -1/2.<br>
cos(A-B) = cos(A)*cos(B)+sin(A)*sin(B)<br>
Plug in the numbers and do the calculation.<br>