Writing Equation from Graph

Pre-Algebra · Axiom Academy

EXAMPLE Writing the Equation of a Line from its Graph Read the y-intercept and the slope straight off a graph, then assemble the slope-intercept equation. The line below is graphed on a coordinate plane. It passes neatly through the lattice points and . Write the equation of this line in slope-intercept form, y = mx + b . Each grid square is one unit. The red dots mark the two points the line passes through. Nice work — you turned a picture of a line into its equation. The recipe is always the same: Read the y-intercept (b): it's the y-value where the line crosses the y-axis. Pick two lattice points: points that land on grid corners keep the arithmetic clean. Slope is rise over run: , subtracting the coordinates in the same order. Assemble: drop m and b into y = mx + b — here . Always sanity-check: both points should satisfy the equation. For (4,3) : . ✓︎

This is the written version of the interactive lesson above. See the full Pre-Algebra course.