Kendall says the sum of (6x2 + 4xy + 2y2) and (4x2 – 2xy – 3y2) is (10x2 + 2xy – 5y2). What error did Kendall make?

Add the coefficients of matching terms: 6x² + 4x² = 10x², and 4xy − 2xy = 2xy. For the y² terms, 2y² − 3y² = −y², not −5y². Kendall combined the like terms 2y² and −3y² incorrectly.

AI-written and checked against the verified answer.