Solve for X Calculator

Solve for x — or y, r, u or any other letter. Type the equation or formula, say which variable you want, and Sumzo isolates it step by step.

the letter to find (x, y, r…)

Tip: use the math keyboard for symbols like √, x² and fractions. You can also attach a photo, screenshot or PDF of the problem (up to 4 files).

Try an example:
Explanation

How to use the variable solver

  1. Type the letter you want in the “Solve for” box — x is already there — then type the equation or formula, such as “2x + 3y = 6”.
  2. Press Solve. Sumzo undoes each operation in turn until the variable is on its own.
  3. With other letters in the equation (a formula), the answer is written in terms of those letters.
  4. Read the check at the end, or ask “Why?” about any step.

Worked examples

Easy: find xx in 7x+4=257x + 4 = 25

  1. Subtract 4 from both sides: 7x=217x = 21.
  2. Divide both sides by 7: x=3x = 3.
  3. Check: 7(3)+4=257(3) + 4 = 25 ✓.

Medium: find yy in 2x+3y=62x + 3y = 6

  1. Subtract 2x2x from both sides: 3y=6−2x3y = 6 - 2x.
  2. Divide both sides by 3: y=6−2x3=2−23xy = \frac{6 - 2x}{3} = 2 - \frac{2}{3}x.
  3. Check with x=3x = 3: the formula gives y=0y = 0, and 2(3)+3(0)=62(3) + 3(0) = 6 ✓.

Hard: find rr in the formula A=πr2A = \pi r^2

  1. Divide both sides by π\pi: r2=Aπr^2 = \frac{A}{\pi}.
  2. Take the square root. A radius can’t be negative, so keep the positive root: r=Aπr = \sqrt{\frac{A}{\pi}}.
  3. Check: π(Aπ)2=π⋅Aπ=A\pi \left(\sqrt{\frac{A}{\pi}}\right)^2 = \pi \cdot \frac{A}{\pi} = A ✓.

Common mistakes when isolating a variable

  • Undoing operations in the wrong order. Undo addition and subtraction before multiplication and division.
  • Dividing only one term: from 3y=6−2x3y = 6 - 2x, divide the whole right side by 3, not just the 6.
  • Forgetting the negative root. x2=9x^2 = 9 gives x=3x = 3 or x=−3x = -3; drop the negative one only when it makes no sense, like a length.
  • Changing the other letters. In a formula, letters such as xx or π\pi stay in the answer — only the variable you are solving for moves.

Frequently asked questions

What does “solve for x” mean?

It means rearranging the equation until xx is on its own on one side, such as x=3x = 3. The other side is the value (or expression) that xx equals.

How do I solve for y?

The same way as for xx: undo each operation around yy, doing the same thing to both sides. In 2x+3y=62x + 3y = 6, subtract 2x2x, then divide by 3 to get y=2−23xy = 2 - \frac{2}{3}x.

Can it isolate a variable in a formula?

Yes. Type the formula and the letter you want, for example “Solve for h: V = πr²h”. The answer is given in terms of the other letters, here h=Vπr2h = \frac{V}{\pi r^2}.

Does it work for other letters, like u?

Yes — any letter. For example “Solve for u: v = u + at” gives u=v−atu = v - at.

Does the solve for x calculator show steps?

Yes. Each step says what was done to both sides, and the answer is checked by substituting it back where possible.

Where can I practise solve for x problems?

Try the linear equations topic in Practice: new questions every time, with hints and worked solutions.