## Tuesday, 24 February 2015

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

1. line 1. ya cant put 3x3x2x-1. it should be 3x3x2 x (-1)

1. at line 3 you should simplify (18x-1) first to -18 so it will be more clear then the last line should be 36-36-18 shich gives - 18

2. wrong from line 1. the answer should have a squared first then mutiply by 2. for the others it should also b squared then multiply and AxBxC then multiply by 3

3. The negative one in line one must be in brackets.

4. The negative one in line one must be in brackets.

5. Line 1= there should be a bracket for '-1' because two signs cannot be written together. It should be 3x3x2x(-1).

1. the square in line 1 is for a and b respectively, not 2 and 3. So it should be a square x 2 and b square x 3.

6. The mistake is in line 1. The person should not get (3x3x2x-1), they should have gotten 3 times a, b, c individually instead of multiplying them all together.

7. This comment has been removed by the author.

8. In line 1 he did 2 times 3 to the power of 3.but it should be 3 to the power of 2 than times 2 same goes for the 3Bto th power of 2
correct ans -12??

1. also the negative and the multiply by -1 should be only -1 have () not the multiplication too?

9. 1) The answer for 2a2 and 3b2 is wrong as you should square the number first before you substitute the values of the unknowns into the equation

2) -1 must be placed in a bracket.

10. There is a mistake in line 1. You can't put a negative number after an operation sign. You should write (-1) instead of just writing -1.

Grp 1

11. In Line 1, the square (2) does not affect the 2, only a (3). Therefore the expression should be 2(3^2) instead of (2*3)^2. The same mistake is present in the second brackets on Line 1, the expression should be 3(2^2) and not (3*2)^2. In the third bracket (also in Line 1), the expression should be (3*3*2*[-1]) instead of (3*3*2*-1) as the negative sign should not be directly beside an operator but separated with a bracket.

12. In Line 1, the square (2) does not affect the 2, only a (3). Therefore the expression should be 2(3^2) instead of (2*3)^2. The same mistake is present in the second brackets on Line 1, the expression should be 3(2^2) and not (3*2)^2. In the third bracket (also in Line 1), the expression should be (3*3*2*[-1]) instead of (3*3*2*-1) as the negative sign should not be directly beside an operator but separated with a bracket.

13. In line 1, they should have converted a*a first instead of 2*a first. Similarly, they should have converted b*b first instead of 3*b first.
Also, at the end of the working they put '*-1' when it should have been '*(-1)'

So i think it should have been 2*(3*3) - 3*(2*2) + (3*3*2*(-1)). ye.

14. The mistake is in line 1. The person should not place the minus sign after the multiplication sign without the brackets. It should be 3x3x2x(-1).

15. In line 1, he should have done 2x3 to the power of 2, with only 3 to the power of 2 instead of (2x3) to the power of 2. It is the same for 3x2 to the power of 2, the power should only be for the 2, not for the whole sum.

16. line 1
they should have squared the alphabets first
should have been square A before multiplying the others and same thing for B

17. In Line 1 he should have squared the variables first THEN multiply it by the constant.

18. Line 1
2a^2 is 2 x (a^2) not (2 x a)^2
3b^2 is 3 x (b^2) not (3 x b) ^2

The power is only applied on only the variable in that example, not the coefficient.

The final answer should be -12

19. The square root is only applicable to a and b not 2a and 3b. -1 is also supposed to be in a bracket.

20. In line 1, the 2a^2-3b^2+3abc should not multiply 2a and 3b first but should a^2 and b^2 first and the -1 should be bracketed

21. The calculations of 2a^2 and 3b^2 is wrong. 2a^2 is actually 2(a^2) and 3b^2 is actually 3(b^2).

(3*3*2*-1) is not correct and must be written as [3*3*2*-1)].

22. In line 1, the power only affects the letter before it, so instead of (2 times 3)to the power of 2, and (3 times 2) to the power of 2, it should be 2 times (3 to the power of 2) and 3 times (2 to the power of 2).

23. The mistake is at line 1. The answers for 2a to the power of 2 and 3b to the power of 2 are not correct. It should be squared first before substituting.

24. the -1s should be in brackets : (-1)

1. should also be 2 (3 to the power of 2)