Chapter 24 ยท ICSE Class 9 Mathematics (Selina Concise)

Graphical Solution

Solve simultaneous linear equations by plotting their graphs and finding the point of intersection.

๐Ÿ“ˆ Chapter 24

The graphical solution of two linear equations, found where their lines cross Two straight lines plotted on a graph, crossing at a single point, which represents the solution that satisfies both equations at once Solution
24.1

Plotting Linear Equations

A linear equation like y=mx+c forms a straight line when plotted, found by calculating y for a few values of x.

1

For y=2x+1, find y when x=0 and x=2.

x=0: y=1; x=2: y=5

2

For x+y=6, find two points on this line.

x=0,y=6 and x=6,y=0 are both solutions

24.2

Finding the Solution by Intersection

The solution to two simultaneous equations is the point where their graphs intersect โ€” this point satisfies both equations.

1

Two lines y=x+2 and y=โˆ’x+6 intersect where?

Setting equal: x+2=โˆ’x+6 โ†’ 2x=4 โ†’ x=2, y=4; intersection is (2,4)

2

Why does the intersection point solve both equations simultaneously?

Because it's the only point that lies on both lines, meaning its coordinates satisfy both equations at once

Practice

Exercises

1. For y=3xโˆ’1, find y when x=0 and x=1.

2. Find two points on the line 2x+y=8.

3. Two lines y=2x and y=x+3 intersect where?

4. Two lines x+y=10 and xโˆ’y=2 intersect where?

5. If two lines are parallel, how many solutions does the simultaneous system have?