# Example 20 - Chapter 10 Class 11 Straight Lines

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

Transcript

Example 20 If the lines 2x + y 3 = 0, 5x + ky 3 = 0 and 3x y 2 = 0 are concurrent, find the value of k. Three lines are concurrent if they pass through a common point i.e. point of intersection of any two lines lies on the third line It is given that lines 2x + y 3 = 0 5x + ky 3 = 0 3x y 2 = 0 are concurrent So, finding point of intersection of lines (1) & (3) Adding (1) & (3) (2x + y 3) + (3x y 2) = 0 2x + 3y + y y 3 2 = 0 5x + 0 5 = 0 5x = 5 x = 5/5 x = 1 Putting x = 1 in (1) 2x + y 3 = 0 2(1) + y 3 = 0 2 + y 3 = 0 y 1 = 0 y = 1 Hence point of intersection of line(1) & (3) is (1, 1) Since lines (1), (2) & (3) are concurrent (1, 1) will satisfy equation of line (2) Putting x = 1 & y = 1 in (2) 5x + ky 3= 0 5(1) + k(1) 3 = 0 5 + k 3 = 0 k + 5 3 = 0 k + 2 = 0 k = 2 Thus, k = -2

Other Type of questions - 3 lines Concurrent

Chapter 10 Class 11 Straight Lines

Concept wise

- Cordinate geometry questions
- Slope - Finding slope
- Slope - Prependicularity
- Angle between two lines by Slope
- Collinearity of 3 points by sliope
- Point Slope form
- Slope-Intercept form
- Intercept form
- Normal form
- Given Statement
- Two lines // or/and prependicular
- Angle between two lines
- Distance - Between two parallel lines
- Distance of a point from a line
- Distance of a point from a line along a line
- Other Type of questions - Area of Triangle formed
- Other Type of questions - 3 lines Concurrent
- Other Type of questions - Image
- Other Type of questions - Mix

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.