高二数学：已知平面向量a,b,c满足|a|=|b|=|c|≠0,且|a-b|=2|b-c|=1,则b*(a-c)=

|a－b|²=1 ===>>> |a|²－2a*b＋|b|²=1 ===>>> 2|b|²－2a*b=1 ==>>>2b*b－2a*b=1 ==>>b*(a－b)=1/2|b－c|²=1/16 ==>> |b|²－2b*c＋|c|²=1/16 ==>>> |b|²－2b*c＋|b|²=1...