SAT Math: Parallel and Perpendicular Lines
36+ practice questions in Praczo
The concept, explained
- 1
Parallel lines have the EXACT SAME slope (m₁ = m₂) but different y-intercepts.
- 2
A system of two parallel lines has NO solution (they never intersect).
- 3
Perpendicular lines have slopes that are NEGATIVE RECIPROCALS (m₁ = -1/m₂). Note: their product is always -1.
- 4
If given an equation in standard form Ax + By = C, the slope is -A/B. Use this to quickly find parallel/perpendicular slopes.
- 5
To find the equation of a parallel/perpendicular line through a specific point, find the new slope and plug it into point-slope form with the given point.
- ✗ Thinking perpendicular slopes are just the reciprocal (forgetting to flip the sign).
- ✗ Assuming two lines with the same slope are parallel without checking the y-intercept (if the intercepts are identical, it's the same line, resulting in infinite solutions, not zero).
SAT-style practice
Given the line 2x + 4y = 8, what is the slope of a line perpendicular to it?
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