Mathematics for IGCSE & O level - Coordinate Geometry (Section 3 - No. 24)
If two lines cross at right angles at the point (3, 3). One passes through (6, 0). What is the equation of the other line?
y = x
y = 2x + 3
y = 3x - 6
y = x + 3
Explanation
The gradient of a line with points (3,3) (6,0) is (0-3)/(6-3)=-1. Since they are at right angles the other gradient is 3. Substituting the point (3,3) in to y=3x+c, 3 = 3(3) +c, c =-6. Then y=3x-6.
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