已知-3已知-3
已知-3由-3-4由-21所以-16<(a-b)*c^2<0.因为-π/2<=α<β<=π/2,所以-π/2<=α<=π/2,-π/4<=β/2<=π/4,所以-3π/4<=α-β/2<=3π/4,-3π/4<=α+β/2<=3π/4.