Module 2 · Algebra Foundations
Chapter 9: Systems of Linear Equations
Algebra
4 topics
What this chapter covers
The 4 topics below make up Systems of Linear Equations on the Digital SAT. Click any topic to open its notes, examples and practice test.
Study material & tests
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Formula Reference Sheet
This chapter
Methods
| Graphical | solution = intersection point of the two lines |
|---|---|
| Substitution | solve one equation for a variable, plug into the other |
| Elimination | add/subtract equations to cancel a variable |
Number of solutions
| One solution | lines cross (different slopes) |
|---|---|
| No solution | parallel lines (same slope, different intercept) |
| Infinite solutions | same line (identical equations) |
Digital SAT reference
Area & Circumference
| Circle area | A = πr² |
|---|---|
| Circle circumference | C = 2πr |
| Rectangle | A = ℓw |
| Triangle | A = ½ b h |
Volume
| Rectangular box | V = ℓwh |
|---|---|
| Cylinder | V = πr²h |
| Sphere | V = 4⁄3 πr³ |
| Cone | V = 1⁄3 πr²h |
| Pyramid | V = 1⁄3 ℓwh |
Right triangles
| Pythagorean theorem | a² + b² = c² |
|---|---|
| 30°–60°–90° | sides x : x√3 : 2x |
| 45°–45°–90° | sides s : s : s√2 |
Constants
| Degrees in a circle | 360° |
|---|---|
| Radians in a circle | 2π |
| Angles of a triangle | sum = 180° |
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