x is an algebraic letter of the alphabet and is not the same thing as the mathematical operator
Mathematics is a language too!
... But that being said... Duolingo doesn't seem to accept those symbols either! (Yet it's more than happy to accept
Looks like there's no lazy shortcut for this one! :'(
If someone is interested, some other math terms (but not only) can be found here (on one place and in different languages):
Für Deutsch Sprechende... Pippi Langstrumpf Lied:
Zwei mal drei MACHT vier, widewidewitt und drei MACHT neune, ich mach mir die Welt, widewide wie sie mir gefällt.
Accepted forms in english: Three times three is nine Three times three makes nine Three times three equals nine In all of these Three BY three is also good. Also Three threes ARE /Make /equal nine (see we have had to go to plural here) Duolingo is just a computer program. The programmers can't be expected to cover EVERY variation in every case! Just accept that if you learn one correct way of saying something you've won
Someone asked for the other math operations. Here you go: l'addizione (addition) due e due fa quattro, due più due è uguale a quattro, due più due fa quattro. la sottrazione (subtraction) la detrazione (also subtraction) otto meno tre è uguale a cinque, otto meno tre fa cinque. la moltiplicazione (multiplication) quattro moltiplicato per due è uguale a otto, quattro per due fa otto. la divisione (division) sei diviso due fa tre.
I like Duolingo, but you're right—they frequently make silly, basic English grammar and syntax errors. Their English translations are often technically correct but awkward, and sometimes just wrong. They need to hire a native English speaking technical writer/editor to check their English translations.