Class 11 Maths Chapter 9 Straight Lines – Revision Notes

Quick revision notes for Class 11 Maths Chapter 9 (Straight Lines). These Class 11 Maths Chapter 9 notes are ideal for quick revision just before exams.

Slope

• m = (y2−y1)/(x2−x1) = tanθ.
• Parallel: m1=m2. Perpendicular: m1×m2=−1.

Equation Forms

• Point-slope: y−y1=m(x−x1).
• Slope-intercept: y=mx+c.
• Intercept form: x/a+y/b=1.
• General form: Ax+By+C=0.

Distance

• Between 2 points: d=√[(x2−x1)²+(y2−y1)²].
• Point from line: d=|Ax1+By1+C|/√(A²+B²).

One-Line Summary

Straight lines are analysed via slope (rate of rise), multiple equation forms depending on given information, and distance formulas for points and lines — with parallel/perpendicular conditions based on slope relationships.

Written by Satish

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