It's correct because that's how it's written down in the textbook! Q.E.D!✨
Most certainly a prove "left hand side" = "right hand side" math question.In Japanese, when marking:
〇 = Correct
✓ = Wrong
X = Wrong
Marking ✓ for wrong answers is usually preferred because it's faster. That X down there was prolly the teacher being frustrated enough (for that particular answer) to go the extra way to mark it X.
