Please help me with this I will give brainliest to one of the two who has the best answer. Thank you!

Answer:
Step-by-step explanation:
(3a-7)²=(3a-7)(3a-7)
= 9a²-21a-21a+49
= 9a²-42a+49
Therefore the error in that answer is -42a was replaced with -21a.
Answer:
(3a-7)²=(3a-7)(3a-7)
= 9a²-21a-21a+49
= 9a²-42a+49
Step-by-step explanation: