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3.3.4

3.3.4. 两条平行直线间的距离. 概念. 两条平行直线间的距离是指夹在两条平行线间公垂线段的长. 两平行线间的距离处处相等. 思考？. 怎样判断两条直线是否平行？. 2. 设 l 1 // l 2 ，如何求 l 1 和 l 2 间的距离？ 1 ）能否将平行直线间的距离转化为点到直线的距离？ 2) 如何取点，可使计算简单？. 例 7 已知直线 和 l 1 与 l 2 是否平行？若平行 , 求 l 1 与 l 2 的距离.

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3.3.4

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  1. 3.3.4 两条平行直线间的距离

  2. 概念 两条平行直线间的距离是指夹在两条平行线间公垂线段的长 两平行线间的距离处处相等

  3. 思考？ • 怎样判断两条直线是否平行？ 2.设l1//l2，如何求l1和l2间的距离？ 1）能否将平行直线间的距离转化为点到直线的距离？ 2) 如何取点，可使计算简单？

  4. 例7 已知直线 和 l1 与l2 是否平行？若平行,求 l1与 l2的距离.

  5. 求证：两条平行直线Ax+By+C1=0和Ax+By+C2=0间的距离为求证：两条平行直线Ax+By+C1=0和Ax+By+C2=0间的距离为

  6. 求平行线2x-7y+8=0与2x-7y-6=0的距离. 两平行线间的距离处处相等 解： 在l2上任取一点，如P(3,0) P到l1的距离等于l1与l2的距离 直线到直线的距离转化为点到直线的距离

  7. 小结 1.平面内一点P(x0,y0) 到直线Ax+By+C=0 的距离公式是 当A=0或B=0时,公式仍然成立. 2.两条平行线Ax+By+C1=0与Ax+By+C2=0的距离是

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