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Reverse FOIL Calculator.

Expand (ax + b)(cx + d) into its quadratic coefficients.

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Set your values

Results update as you type.

02 / ANSWER

First x coefficient

First constant

Second x coefficient

Second constant

Coefficient 1 must be finite.

Results update automatically as you type.

Use Cases

Check your algebra homework

Quickly verify if you expanded a product of two binomials correctly. Enter the binomials and compare the result with your own work.

Example: For (x+3)(x-2), enter 1, 3, 1, -2 to get x^2 + x - 6.

Simplify expressions for graphing

When you need the standard form of a quadratic to find its vertex or roots, this calculator expands the factored form instantly.

Example: Convert (2x-1)(x+4) to 2x^2 + 7x - 4.

Frequently Asked Questions

What does the reverse foil calculator do?: This calculator takes two binomials, each with an x coefficient and a constant, and multiplies them using the FOIL method. It returns the expanded quadratic polynomial in standard form, showing the combined x term and constant.
How do I enter the binomials?: For each binomial, enter the coefficient of x (the number multiplying x) and the constant term. For example, for (3x + 2), enter 3 as the x coefficient and 2 as the constant. The calculator will multiply the two binomials and show the result.
Can the calculator handle negative numbers?: Yes, you can enter negative numbers for any of the coefficients or constants. The calculator will correctly apply the signs during multiplication and simplify the result.

Tips & Common Mistakes

Tips

Double-check that you entered the coefficients and constants in the correct order: first x coefficient, first constant, second x coefficient, second constant.
Use the FOIL method mentally: multiply First, Outer, Inner, Last terms, then combine like terms. This calculator does that for you.
If you have a binomial like (x+5), remember the x coefficient is 1, so enter 1 for the x coefficient.
For expressions with subtraction, enter the negative sign with the number, e.g., (x-3) means constant is -3.

Common Mistakes to Avoid

Entering the constant as a positive number when the binomial has a minus sign, e.g., entering 3 instead of -3 for (x-3).
Confusing the order of the fields: the calculator expects the x coefficient first, then the constant for each binomial.
Forgetting that a variable without a coefficient has an implied coefficient of 1, so entering 0 instead of 1 will change the result.

Last updated: August 13, 2026

Use Cases

Check your algebra homework

Quickly verify if you expanded a product of two binomials correctly. Enter the binomials and compare the result with your own work.

Example: For (x+3)(x-2), enter 1, 3, 1, -2 to get x^2 + x - 6.

Simplify expressions for graphing

When you need the standard form of a quadratic to find its vertex or roots, this calculator expands the factored form instantly.

Example: Convert (2x-1)(x+4) to 2x^2 + 7x - 4.

Frequently Asked Questions

What does the reverse foil calculator do?

This calculator takes two binomials, each with an x coefficient and a constant, and multiplies them using the FOIL method. It returns the expanded quadratic polynomial in standard form, showing the combined x term and constant.

How do I enter the binomials?

For each binomial, enter the coefficient of x (the number multiplying x) and the constant term. For example, for (3x + 2), enter 3 as the x coefficient and 2 as the constant. The calculator will multiply the two binomials and show the result.

Can the calculator handle negative numbers?

Yes, you can enter negative numbers for any of the coefficients or constants. The calculator will correctly apply the signs during multiplication and simplify the result.

Tips & Common Mistakes

Tips

Double-check that you entered the coefficients and constants in the correct order: first x coefficient, first constant, second x coefficient, second constant.
Use the FOIL method mentally: multiply First, Outer, Inner, Last terms, then combine like terms. This calculator does that for you.
If you have a binomial like (x+5), remember the x coefficient is 1, so enter 1 for the x coefficient.
For expressions with subtraction, enter the negative sign with the number, e.g., (x-3) means constant is -3.

Common Mistakes to Avoid

Entering the constant as a positive number when the binomial has a minus sign, e.g., entering 3 instead of -3 for (x-3).
Confusing the order of the fields: the calculator expects the x coefficient first, then the constant for each binomial.
Forgetting that a variable without a coefficient has an implied coefficient of 1, so entering 0 instead of 1 will change the result.

Use Cases

Check your algebra homework

Quickly verify if you expanded a product of two binomials correctly. Enter the binomials and compare the result with your own work.

Example: For (x+3)(x-2), enter 1, 3, 1, -2 to get x^2 + x - 6.

Simplify expressions for graphing

When you need the standard form of a quadratic to find its vertex or roots, this calculator expands the factored form instantly.

Example: Convert (2x-1)(x+4) to 2x^2 + 7x - 4.

Frequently Asked Questions

What does the reverse foil calculator do?

How do I enter the binomials?

Can the calculator handle negative numbers?

Yes, you can enter negative numbers for any of the coefficients or constants. The calculator will correctly apply the signs during multiplication and simplify the result.

Tips & Common Mistakes

Tips

Double-check that you entered the coefficients and constants in the correct order: first x coefficient, first constant, second x coefficient, second constant.
Use the FOIL method mentally: multiply First, Outer, Inner, Last terms, then combine like terms. This calculator does that for you.
If you have a binomial like (x+5), remember the x coefficient is 1, so enter 1 for the x coefficient.
For expressions with subtraction, enter the negative sign with the number, e.g., (x-3) means constant is -3.

Common Mistakes to Avoid

Entering the constant as a positive number when the binomial has a minus sign, e.g., entering 3 instead of -3 for (x-3).
Confusing the order of the fields: the calculator expects the x coefficient first, then the constant for each binomial.
Forgetting that a variable without a coefficient has an implied coefficient of 1, so entering 0 instead of 1 will change the result.