In △ ABC, cos (PI / 4 + a) = 5 / 13, then sin2a=
sin( pi/4 +A)=12/13
2cos( pi/4 +A)*sin( pi/4 +A)=2*5/13*12/13
sin(pi/2+2A)=120/169
cos2A=120/169
sin2A=119/169
RELATED INFORMATIONS
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