这部分需要会什么？
- 使用对顶角、邻补角和平行线角关系
- 求三角形与多边形内角
- 把图中的角关系转为方程
核心概念与公式
对顶角相等，组成平角的邻角之和为 \(180^\circ\)，围绕一点的角之和为 \(360^\circ\)。两条平行线被截时，同位角和内错角相等，同旁内角互补。
三角形内角和为 \(180^\circ\)，一个外角等于不相邻两内角之和。\(n\) 边形内角和为 \((n-2)180^\circ\)；正 \(n\) 边形每个内角为该总和除以 \(n\)，每个外角为 \(360^\circ/n\)。
做题时怎样使用
- 先标出已知平行、垂直、等腰等条件
- 用最直接的角关系建立等式
- 算出角后检查它属于内角、外角还是补角，并确认大小合理
容易混淆的地方
只有给出或证明平行时，才能使用平行线的对应角关系；不能仅凭图看起来平行。多边形内角相等也需要正多边形等条件。
用一个例题串起方法
知识点教学例题三角形一个外角为 \(125^\circ\)，不相邻的两个内角分别为 \((2x+5)^\circ\) 和 \(3x^\circ\)。求 \(x\)。
展开解题思路 ＋
外角等于两不相邻内角之和，因此 \(2x+5+3x=125\)，得到 \(x=24\)。两个内角为 \(53^\circ\)、\(72^\circ\)，第三个为 \(55^\circ\)。
本知识点题库
先独立作答，再查看答案与解析。
直线・角与多边形进阶
In the figure shown, lines l and k are parallel and line t intersects both lines. If \( x>134 \), which of the following must be true?
原库参考解析
直线・角与多边形挑战
In triangle \( JKL \), the measures of \( ∠K \) and \( ∠L \) are each 51. What is the measure of \( ∠J \) , in degrees? (Disregard the degree symbol when entering your answer.)
原库参考解析
直线・角与多边形进阶
In \( \triangle JKL \), the measures of both \( ∠J \) and \( ∠K \) are equal and the measure of \( ∠L \) is \( 138^{∘} \) . What is the measure of \( ∠J \) ?
原库参考解析
直线・角与多边形进阶
In triangle ABC, the measure of angle A is \( 56^{∘} \), the measure of angle B is \( 90^{∘} \), and the measure of angle C is \( (\frac{k}{2})^{∘} \). What is the value of k?
原库参考解析
直线・角与多边形挑战
In triangle ABC, the measure of angle A is \( 49^{∘} \) , the measure of angle B is \( 90^{∘} \), and the measure of angle C is \( (\frac{k}{2})^{∘} \). What is the value of k?
原库参考解析
直线・角与多边形进阶
In \( \triangle ABC \) , the sum of the measures of \( ∠A \) and \( ∠B \) is 159.5°. What is the measure of \( ∠C \)?
原库参考解析
直线・角与多边形基础
In the figure shown, d, e, and f are constants and the value of k is 2. If the measure of angles D, E, and F are 42°, x°, and (2x + 12)°, respectively, what is the measure, in degrees, of angle S?
原库参考解析
直线・角与多边形进阶
In the figure, line j is parallel to line k. What is the value of x?
原库参考解析
直线・角与多边形进阶
For isosceles triangle \( ABC \), \( AB=BC=56 \), the measure of angle \( ABC \) is \( 36^{∘} \), point \( D \) lies on \( BC \), and \( ∠BAC \) is bisected by \( AD \). Which of the following statements must be true?
原库参考解析
直线・角与多边形挑战
In the figure, line \( AB \) is parallel to line \( CD \), and line \( AD \) intersects line \( BC \) at point \( E \). If \( y=118 \) and \( z=116 \), what is the value of x?
原库参考解析
直线・角与多边形进阶
In the figure, lines a and b are parallel and line c intersects both lines. If \( r=9k-10 \) and \( s=7k-98 \), what is the value of t?
原库参考解析
直线・角与多边形挑战
In the figure, line \( AB \) is parallel to line \( CD \), and line \( AD \) intersects line \( BC \) at point \( E \). If \( y=115 \) and \( z=118 \), what is the value of x?
原库参考解析
