对于三条线段a、b、c在同一条直线上的等积式b2=ac的证明,常常因为找不到平行线或相似三角形而使思路中断,这时候若能适当运用代换法,可使思路延续,问题迎刃而解.一、等线段代换法一般证题思路:要证b2=ac,改证a:b=b:c,为此先证a:m=m:c,即m2=ac;再证m=b,即可.例1已知:如图1,在△ For the proof of the isomorphic b2=ac of the three line segments a, b, c on the same line, the line of thought is often interrupted because no parallel lines or similar triangles are found. If the substitution method can be used properly, this can be used. Continuation of ideas, the problem solved. First, the line substitution method general testimony ideas: to prove b2 = ac, change the certificate a: b = b: c, for this proving a: m = m: c, that is m2 = ac ; reprove that m=b, can be. Example 1 is known: as shown in Figure 1, at △