1.δ≤0 16sin^2c-24cosc≤0 2-2cos^2c-3cosc≤0 解得cosc≥0.5 又c∈(0,π) 所以c最大为π/32.a=2b sina=2sinb 又a+b=2π/3 sin(2π/3 -b)=2sinb 即根号3sinb-cosb=0 所以tanb=1/根号3b∈(0,π) b=π/6
