Straight lines

Geometry Level 2

What is the equation of a straight line which is perpendicular to the straight line 2 x + 3 y + 5 = 0 2x+3y+5=0 and passes through the point ( 2 , 4 ) (-2,-4) ?

3 x 2 y = 0 3x-2y=0 3 x 2 y 2 = 0 3x-2y-2=0 y = 2 3 x + 2 y=\frac 23x+2 3 y 2 x + 2 = 0 3y-2x+2=0

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2 solutions

Chew-Seong Cheong
May 18, 2017

Given the line 2 x + 3 y + 5 = 0 y = 2 3 x 5 3 2x+3y+5 = 0 \implies y = -\dfrac 23x - \dfrac 53 . Therefore, the gradient of the line is 2 3 -\dfrac 23 . Let the perpendicular line be y = m x + c y = mx + c . where m m and c c are the gradient and x x -intercept. Then 2 3 m = 1 -\dfrac 23 m = - 1 , m = 3 2 \implies m = \dfrac 32 . Since the line passes through the point ( 2 , 4 ) (-2,-4) , then 4 = 3 2 ( 2 ) + c -4 = \dfrac 32(-2)+c , c = 1 \implies c = - 1 . Therefore, the line is y = 3 2 x 1 y = \dfrac 32x-1 , 3 x 2 y 2 = 0 \implies \boxed{3x - 2y-2 = 0} .

Tahmid Chowdhury
May 18, 2017

Perpendicular line to the straight line 2x+3y+5=0 is 3x-2y+k=0---(1).As the point passes through (-2,-4),we get from the equation (1)-3.(-2)-2.(-4)+k=0;k=-2. So putting value of k in (1),we get the required equation 3x-2y-2=0.

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