Find my mistake
Enter your working line by line, typed or pasted straight out of a PDF as LaTeX. We point at the first line that does not follow and prove it with numbers you can check by hand. A line is never called wrong without that proof.
Each line must equal the line above it. You may also chain several expressions on one line with equals signs.
How this works
You never start from nothing
Each new line begins as a copy of the line above, so you change only what changed. You can also say a line out loud, or paste your whole working at once.
Every line is read back
What we understood is shown as typeset mathematics beside each line, so you can see we read what you meant before anything is judged.
A tick, or a proof
A tick appears beside every line that follows. The first line that does not is pointed out, with numbers you can put in by hand to watch it fail.
Never wrong without proof
When we cannot certify a step we say so plainly instead of guessing. A correct line is never called a mistake.
How to type mathematics
Powers and roots
x^2 for a power, sqrt(x + 1) for a root, x^(1/3) for a cube root.
Fractions
Use a slash and brackets: (x + 1)/(x - 2). Decimals such as 0.25 are held exactly.
Functions
sin(2x), cos(x), tan(x), ln(x), e^(-x), always with brackets. sin^2(x) is understood.
Complex numbers
Write i for the imaginary unit: (2 + 3i)(1 - i). Square roots of negative numbers become multiples of i.
Or paste LaTeX
Copy a line straight out of a paper or your notes, dollar signs and all. A command we do not know stops the reading and says which one, rather than quietly dropping it and checking something you did not write.