f(x)=m*n=根号3sinxcosx-1/2cos2x=根号3/2sin2x-1/2cos2x=sin(2x-Pai/6)
f(A)=sin(2A-Pai/6)=1
2A-Pai/6=Pai/2
A=Pai/3
a^2=b^2+c^2-2bccosA
49=25+c^2-10c*1/2
c^2-5c-24=0
(c-8)*(c+3)=0
c=8
f(x)=m*n=根号3sinxcosx-1/2cos2x=根号3/2sin2x-1/2cos2x=sin(2x-Pai/6)
f(A)=sin(2A-Pai/6)=1
2A-Pai/6=Pai/2
A=Pai/3
a^2=b^2+c^2-2bccosA
49=25+c^2-10c*1/2
c^2-5c-24=0
(c-8)*(c+3)=0
c=8