(1)
m*n=1
-cos^2A/2+sin^2A/2=-cosA=1/2
A=120°
(2)
S=√3=0.5bcsinA
bc*√3/2=2√3
bc=4
a^2=b^2+c^2-2bccosA=b^2+c^2+bc
b^2+c^2=12-4=8
(b+c)^2=b^2+c^2+2bc=8+8=16
b+c=4
a+b+c=4+2√3
S=0.5r(a+b+c)=2√3
r=4√3/(4+2√3)
=4√3(4-2√3)/(16-12)
=2√3(2-√3)
=4√3-6
(1)
m*n=1
-cos^2A/2+sin^2A/2=-cosA=1/2
A=120°
(2)
S=√3=0.5bcsinA
bc*√3/2=2√3
bc=4
a^2=b^2+c^2-2bccosA=b^2+c^2+bc
b^2+c^2=12-4=8
(b+c)^2=b^2+c^2+2bc=8+8=16
b+c=4
a+b+c=4+2√3
S=0.5r(a+b+c)=2√3
r=4√3/(4+2√3)
=4√3(4-2√3)/(16-12)
=2√3(2-√3)
=4√3-6