A student submitted the following problem

Question

A student submitted the following problem, but the solution is incorrect. • Identify the mistake. What did the student do wrong? • Solve the problem correctly. Sec. 12.5 #86 Simplify: 12c2 d – 2cd + 8cd2 – (-c2 d + 4cd) – (5cd – 2cd2 ) Incorrect solution: 12c2 d – 2cd + 8cd2 – (-c2 d + 4cd) – (5cd – 2cd2 ) 12c2 d – 2cd + 8cd2 – c2 d + 4cd – 5cd – 2cd2 12c2 d + 6cd2 –c2 d – 3cd 

 

Answer 1

The reason that this student's answer is incorrect is because he/she did not correctly distribute the "minus" sign to all of the variables in parentheses. The student also failed to combine all of the like terms. The correct final answer is:

13c²d - 11cd + 10cd²

You can get this by combining the following terms:

(A) 12c²d - (-c²d) = 12c²d + c²d = 13c²d

(B) -2cd - 4cd - 5cd = -11cd

(C) 8cd² - (-2cd²) = 8cd² + 2cd² = 10cd²

If you have any follow up questions then please ask! :)

Answer 2

12c²d – 2cd + 8cd² – (-c²d + 4cd) – (5cd – 2cd²)

12c²d – 2cd + 8cd² + c²d - 4cd – 5cd + 2cd²

Can you collect like terms and answer?