在三角形ABC中,abc分别是ABC的对边,且a²+c²-b²=-ac,求角B的大小
在三角形abc中,a,b,c分别为角a,b,c的对边。如果a,b,c成等差数列,角b=30度,三角形abc面积为3/2,求b的值s=acsinb/2=3/2,ac=6,
a
c=2b,a^2
2ac
c^2=4b^2,a^2
c^2-b^2=3b^2-12.
cosb=(a^2
c^2-b^2)/(2ac)=√3/2,
(3b^2-12)/12=√3/2,
b^2=2√3
4,
b=√3
1.
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