4. For triangle ABC,show that
(i) sin A+B /2 = cos C/2
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sin(A+B/2)=cosC/2
A+B+C=180 (sum of angles of a triangle=180)
A+B=180-C
A+B/2=180-C/2
=180/2-C/2
=(90-C/2)
SUBSTITUTION....
sin(90-C/2) since,sin(90-A)=cos A
=cosC/2
LHS=RHS
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