Linear Equation Solver

Quick start

1. Match your equation to ax + b = c. For 4x − 9 = 15, enter a = 4, b = −9 and c = 15.
2. Read the two steps: subtract b from both sides, then divide both sides by a.
3. The final line gives x, as a fraction too when the answer is not a whole number.

The idea: keep the equation balanced

An equation is like a balance scale. Whatever you do to one side, you must do to the other. To get x alone, undo the operations in reverse order. In ax + b = c, x was multiplied by a and then b was added, so you take away b first and divide by a last.

Example: 4x − 9 = 15

Add 9 to both sides: 4x = 24. Divide both sides by 4: x = 6. Check by substituting: 4 × 6 − 9 = 24 − 9 = 15. Both sides match.

Special cases

If a is 0, x disappears. When b and c are then equal, such as 0x + 5 = 5, every number works. When they differ, such as 0x + 5 = 8, no number works. The solver tells you which case you have.

Rearranging first

If x appears on both sides, collect it first. 5x + 2 = 3x + 10 becomes 2x + 2 = 10, so enter a = 2, b = 2 and c = 10 to get x = 4.

Common questions