Key Concepts: Equations of Lines

Slope-Intercept Form

y = mx + b

where m is the slope and b is the y-intercept.

Point-Slope Form

y − y₁ = m(x − x₁)

where m is the slope and (x₁, y₁) is a known Point on the Line.

Standard Form

Ax + By = C

where A, B, and C are integers and A ≥ 0.

Writing Equations

• Given slope and y-intercept → use slope-intercept form.
• Given slope and a Point → use Point-slope form.
• Given two points → find slope first, then use Point-slope form.
• Parallel to a given Line → same slope, different intercept.
• Perpendicular to a given Line → use negative reciprocal slope.