## Monday, 24 February 2014

### Substitution: Can you tell What's Wrong? (1)

#### 9 comments:

1. Line 1, 2a^2 is not (2*a)2 it is 2*(a^2). This is the same with 3b^2.
Line 2 would have been (2*18) - (3*4)+(9*2*-1)
Line 3 would have been 36 - 12 + (-18)
Therefore the answer would have been 6

1. Sorry line 1 should not have been (2*a)^2 and not (3*b)^2, It should have been 2*(a^2)

2. The answer is not correct either, it should be -12

2. Firstly, 2a^2 is 2*3^. But this student has written it as (2*3)^. So this student has added an extra 2^ into the equation. This student has made so many in line 1 and they are all the same error category.

3. In line 1, 2a^2 is 2*a^2, not (2a)^2. So everything is wrong already.

4. Line 1 is wrong as it requires a to be squared before being multiplied by 2.
b needs to be squared before being multiplied by 3.
a, b and c need to be multiplied together before being multiplied by 3.
This will subsequently affect all other working.

5. In line 1, it should not be (2x3)^2 but 2x3x3. Same for (3x2)^2 but 3x2x2.
So in line 2, it should be 18 - 12 instead of 6^2 - 6^2.
Line 3, it should be 6 + (18 x -1)
In Line 4, the answer is -12

1. There has to be a bracket before -1.

6. In line 1, it is supposed to be (2 x a x a). There should have been a bracket around (-1).