这部分需要会什么？
- 根据对应角或对应边判定相似
- 按顶点顺序写出正确的边长比例
- 区分相似比例与全等关系
核心概念与公式
相似三角形对应角相等、对应边成比例。常用判定包括两角相等（AA）、两组对应边成比例且夹角相等（SAS）、三组对应边成比例（SSS）。全等图形形状和大小都相同，对应边比为 1。
若 \(\triangle ABC\sim\triangle DEF\)，顺序表示 \(A\leftrightarrow D\)、\(B\leftrightarrow E\)、\(C\leftrightarrow F\)。长度倍率为 \(k\) 时，周长倍率为 \(k\)，面积倍率为 \(k^2\)。
做题时怎样使用
- 先从角标记或题目给出的顶点顺序找对应关系
- 用同一方向写各组边长比，并选已知量最多的一组
- 求面积时将长度倍率平方；需要全等时进一步检查倍率是否为 1
容易混淆的地方
两条边的比值相同，并不足以单独证明三角形相似。不要按图上“左边、右边”机械配对，图形可能旋转或翻转。
用一个例题串起方法
知识点教学例题两个相似三角形的对应边长为 6 和 9。较小三角形的面积为 20，求较大三角形的面积。
展开解题思路 ＋
从小到大的长度倍率为 \(9/6=3/2\)，面积倍率为 \((3/2)^2=9/4\)。较大面积为 \(20\times9/4=45\)。
本知识点题库
先独立作答，再查看答案与解析。
相似・全等与比例线段进阶
Triangle \( ABC \) is similar to triangle \( XYZ \), where \( A \), \( B \), and \( C \) correspond to \( X \), \( Y \), and \( Z \), respectively. In triangle \( ABC \), the length of \( AB \) is 170 and the length of \( BC \) is 850. In triangle \( XYZ \), the length of \( YZ \) is 60. What is the length of \( XY \) ?
原库参考解析
相似・全等与比例线段基础
Triangles \( ABC \) and \( DEF \) are congruent, where \( A \) corresponds to \( D \), and \( B \) and \( E \) are right angles. The measure of angle \( A \) is 18°. What is the measure of angle \( F \)?
原库参考解析
相似・全等与比例线段挑战
Triangles \( ABC \) and \( DEF \) are congruent, where \( A \) corresponds to \( D \), and \( B \) and \( E \) are right angles. The measure of angle \( A \) is 18°. What is the measure of angle \( F \)?
原库参考解析
相似・全等与比例线段进阶
Triangles \( ABC \) and \( DEF \) are congruent, with \( A \) corresponding to \( D \), and \( B \) and \( E \) being right angles. The measure of \( A \) is \( 27^{∘} \). We need to find the measure of \( F \).
原库参考解析
相似・全等与比例线段基础
In the figure shown, \( WZ \) and \( XY \) intersect at point \( Q \), \( YQ=21 \) , \( WQ=70 \), \( WX=60 \) , and \( XQ=120 \). What is the length of \( YZ \)?
原库参考解析
相似・全等与比例线段挑战
In the figure shown, \( WZ \) and \( XY \) intersect at point \( Q \), \( YQ=21 \) , \( WQ=70 \), \( WX=60 \), and \( XQ=120 \). What is the length of \( YZ \)?
原库参考解析
相似・全等与比例线段挑战
In triangles LMN and RST, angles L and R each have measure 60°，LN = 10, and RT=30.Which additional piece of information is sufficient to prove that triangle LMN is similar to triangle RST?
原库参考解析
相似・全等与比例线段基础
In triangles ABC and DEF, angles B and E each have measure 27° and angles C and F each have measure 41 °. Which additional piece of information is sufficient to determine whether triangle ABC is congruent to triangle DEF?
原库参考解析
相似・全等与比例线段挑战
Triangle XYZ is similar to triangle RST such that X,Y , and Z correspond to R, S, and T,respectively. The measure of ∠Z is 20° and 2XY = RS. What is the measure of ∠T?
原库参考解析
相似・全等与比例线段进阶
Triangles ABC and DEF are congruent, where A corresponds to D, and B and E are right angles. The measure of angle A is 18°. What is the measure of angle F?
原库参考解析
相似・全等与比例线段进阶
Right triangles PQR and STU are similar, where P corresponds to S. If the measure of angle Q is 18°， what is the measure of angle S?
原库参考解析
相似・全等与比例线段基础
\( \triangle QPR \) is similar to \( \triangle STR \). The lengths represented by \( ST \) , \( QP \) , \( PR \) , and \( QR \) in the figure are 14, 15, 20, and 25, respectively. What is the length of \( SR \) ?
原库参考解析
