∠B=1/2(∠A+∠C)
A+B+C=180
B=60 A+C=120
sinA*sinC=1/2*[cos(A-C)-cos(A+C)]=cos^2B=1/4
得：cos(A-C)=1/2 + cos(A+C)=1/2 -cosB=0;
則|A-C|=90
不妨設(shè)A>C;則A-C=90°.
又由 A+C=120 得
A=105°; C=15°
∴ a/c=sinA/sinC=sin(90°+15°)/sin15°=cos15°/sin15°=tan15°
=(1-cos30°)/sin30°=(1-√3/2)/(1/2)=2-√3.
即a=(2-√3)c.①
由正弦定理得:S=(1/2)·ac·sinB=(√3/4)·ac
即(√3/4)·ac=4√3;
a·c=16 ②
由①②解得:
a=2√6-2√2; c=2√2+2√6;
而b=(sinB/sinC)·c=[(√3/2)/sin(60°-45°)]·(2√2+2√6)
=[(√3/2)/(sin60°·cos45°-cos60°·sin45°)]·(2√2+2√6)
=√3.
a=2√6-2√2; b=√3; c=2√2+2√6;