∵B=2A.∴sin2A=√3sinA,∵sin2A=2sinAcosA，(正弦的二倍脚本公式），sinA≠0∴cosA=√3/2∴A=30º
b=a√3, a/sinA=b/sinB, a/sinA=a√3/sin2A, sin2A/sinA=√3, 2sinAcosA/sinA=√3,
cosA=√3/2, A=π/6
