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Linear Equation Solver – ax + b = 0 Steps

Quick answer

Solve ax+b=0 directly: x=−b/a.

  • Handles fractions, decimals and the a=0 edge cases — 3x+12=0 gives x=−4, verified by substitution.

Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.

How the Linear Equation Solver Works

ax + b = 0 ⇒ x = -b/a

A linear equation in one variable isolates x in a single move: subtract b, then divide by a. Take 3x + 12 = 0. Subtract 12 from both sides to get 3x = -12, then divide by 3, giving x = -4. Verification by substitution returns 3(-4) + 12 = -12 + 12 = 0, confirming the root. The solver handles fractional coefficients such as (2/3)x - 4 = 0, where multiplying both sides by 3/2 yields x = 6, and decimals like 0.5x = 7 with x = 14. Edge cases are flagged explicitly: if a = 0 and b ≠ 0 the equation has no solution (0x = -b is impossible), while a = 0 and b = 0 is an identity true for every x. Each transformation is printed so the method mirrors standard algebra classwork.

  1. 1

    Enter a and b

    Type the coefficients of ax + b = 0

  2. 2

    Isolate the x term

    Subtract b from both sides: ax = -b

  3. 3

    Divide by a

    Compute x = -b/a, exact or decimal as needed

  4. 4

    Verify the solution

    Substitute x back; the left side must equal 0

Use Cases

Break-Even Price

Solve 25x - 1500 = 0 to find 60 units cover a 1,500 fixed cost

Temperature Conversion

Find when °C equals °F: solve 1.8x + 32 = x, giving x = -40

Budget Lines

Determine the quantity where income equals expense

Tips

  • 1

    One linear equation in one unknown always has exactly one root when a ≠ 0

  • 2

    Fractional coefficients clear instantly when you multiply by the LCD

  • 3

    Substitution is the fastest error check for any solved x

Common Mistakes

  • Dividing only the bx side by a and leaving b undivided

  • Sign slip moving b across the equals sign: 3x = -12, not +12

  • Missing the a = 0 special cases — no solution or infinitely many

  • Rounding decimals too early and losing exact checks

FAQs

How do I solve 3x + 12 = 0?

x = -b/a = -12/3 = -4. Check: 3(-4) + 12 = 0.

What if a equals 0?

0x + b = 0 has no solution when b ≠ 0, and infinitely many when b = 0 — every x satisfies it.

How do I handle fractions like (2/3)x - 4 = 0?

Multiply both sides by 3/2 (or add 4 then multiply): x = 4 × 3/2 = 6.

Where do Celsius and Fahrenheit meet?

Solve 1.8x + 32 = x: 0.8x = -32, x = -40. Both scales read -40°.

Does the solver show steps?

Yes — isolation, division and the substitution check are printed for every equation.