Tuesday, 10 January 2012

What is wrong?

Question 1
Describe what's wrong with the working and/or answer.
Suggest how it should look like.


  1. The question is 9w^2 -24w + 16
    Thus, we must do quadratic method to solve the question since there are 3 expressions.

    Thus the answer will be (3w + 4)^2.

    The student however split expanded each expression instead of the whole equation and thus got the wrong answer.

  2. It was a transfer error as (3w)^2-2(12w)+(4)^2 does not equals to (3w-8)^2 it should have been (3w-4)^2


  3. This person has used the equation: a^2-2ab+b^2 = (a-b)^2 to solve this question. The 'a' in this equation is 3w, the 'b' is supposed to be 4, however, this person did not copy the (4)^2 in the 1st line of his/her working to the final answer, and instead copied 8 as the 'b', and as such, this was a careless mistake.

  4. The student should have used shoelace method, instead of that he used the parking lot method.

  5. He missed out the 2x4x12, then 8 came out of nowhere, i suppose it was a transfer error from the 4 square.

  6. The student didn't do proper factrisation. If you use the cross method, your answer will be (3w-4)square.

  7. The student did not factorise correctly; the shoelace method would be a good method to use for this question. The answer would be (3w-4)^2.