### What's Wrong? Q10 (Type 2)

Describe what's wrong with the working and/or answer.
Suggest how it should look like.

1. The answer is suppose to be (3x-8y)^2

2. (3x)^2 - 2(24xy) + (8y)^2 ≠ (3x+8y)^2
= (3x-8y)^2

Owen and shawn kit btwfyi.

3. in this situation, it should be (a-b)^2.
as a is 3x and b is 8y, it should be (3x-8y)^2 instead of (3x+8y)^2

4. Whats wrong: operation error
How it should look like: = (3x-8y)^2

Sandy and Ruoyu

5. Mavis &amp; Qianhui8/17/2011 08:17:00 AM

This is a type 2 question and it should be in a (a-b)^2 format and not in a (a+b)^2 format .
Final answer : (3x-8y)^2

6. M4®k †å¥ &amp; Yi De8/17/2011 08:18:00 AM

This is a type 2 question, therefore the answer should be in (a-b)^2 format. So the answer should be (3x - 8y)^2, not (3x + 8y)^2.

7. Yi Chieh,Kai En, Jiajun

The answer should be (3x-8y)^2 because it follows the pattern of (a-b)^2.

8. (abhi and toby)

9. Matthew and Wei Siew8/17/2011 08:20:00 AM

This student's working is correct, however his/her answer is wrong. The answer should be "(3x - 8y)^2" and not "(3x + 8y)^2" as the formula is (a-b)^2 = a^2 = 2ab + b^2

The answer should be ->
9x^2 - 48xy + 64y^2
= (3x)^2 - 2(24xy) + (8y)^2
= (3x - 8y)^2