Worked example 1 Find the the slope and the y -intercept of the following lines. (i) 5 y = − 2x − 10
Solution
(ii) 3x − 2y + 6 = 0
(–)(–) = +
The y intercept is the point where the line crosses the y -axis.
To investigate if a point is on a line
We mentioned earlier that an equation of a line is a formula where every point on that particular line satisfi es the formula.
Investigating if a point is on a line Substitute the coordinates of the point in for x and y in the equation of the line.
1
2
If the equation is satisfi ed, it is balanced. That is, if the left-hand side (LHS) equals the right-hand side (RHS) then the point is on the line.
Collinear points are points that all lie on the same line. A
Worked example 2 (i) Show that the line 2x + 3y + 4 = 0 passes through the point (–5, 2). (ii) Investigate whether the point (3, –4) is on the line 3x + y − 6 = 0 .