Lesson 02 · Intersection on the plane

Solving by Graphing

Solve a linear system by finding the ordered pair shared by both graphs, then verify that the visual intersection really satisfies both equations.

The learner question

How can the graph solve both equations at once?

Each graph shows every solution to one equation. Their intersection automatically keeps only the ordered pairs that belong to both solution sets.

Graphing method
graph A → graph B → read A ∩ B

The method changes the representation, not the definition of a system solution.

Worked model

The crossing point is a candidate. Both equations verify it.

For y = x + 1 and y = −x + 5, the graphs cross at (2, 3). Reading the graph gives the candidate; substitution explains why it is valid.

A: y = x + 1B: y = −x + 5
intersection (2, 3)
01

Graph both equations

Every point on each line satisfies its own equation.

02

Read the intersection

The lines share the point (2, 3).

03

Verify both constraints

3 = 2 + 1 and 3 = −2 + 5, so the point survives both equations.

Intersection lab

Locate the point shared by both lines.

A: y = x + 1B: y = −x + 5
Choose the intersection
Boundary of the method

A graph can reveal structure without always revealing exact coordinates.

The system y = x and y = −x + 1 intersects at (1/2, 1/2). On a coarse grid that location may only be estimated. Substitution and elimination can recover exact coordinates when the graph is visually ambiguous.

Transfer checkFresh cases, same shared-solution idea
Solving by Graphing check1 / 3

When solving a system by graphing, what point are you looking for?