a的平方-2bc=b的平方-2ac,
=>a^2-b^2=2bc-2ac
=>(a+b+2c)(a-b)=0
=>a-b=0
=>三角形ABC为等腰三角形.=>a^2-b^2=2bc-2ac怎么变成的=>(a+b+2c)(a-b)=0a^2-b^2=2bc-2ac=>(a+b)(a-b)=-2c(a-b)=>(a+b+2c)(a-b)=0