How do you represent an equal number? With an equal sign.
It's worth pointing out that this is a pretty formal word that's used in advanced math. In everyday conversation, people would use イコール for the equal sign.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
You forgot to write an equal sign here.
Koichi feels sick if the top and bottom lines of an equal sign are not the same length.
You have to pay attention to whether the formula to the right of the equal sign is plus or minus.