(sinA)^2-(cosA)^2=1/2
(sinA)^2-[1-(sinA)^2]=1/2
2(sinA)^2=3/2
sinA=√3/2
cosA=1/2
∠A=60°
∠B+∠C=120°
1:当ABC为等边三角形时,a=b=c,b+c=2a
2:当ABC为直角三角形时,a^2+b^2=c^2
2b=c
2b+b=b+c>a
a^2=c^2-b^2=(c+b)(c-b)=3b*b=3b^2
a=√3b
2a=2√3b
b+c=3b
2a>b+c
根据这两种情况,答案应该是C:b+c小于等于2a