**Objectives**:

to clarify, consolidate and analyse common conceptual and careless errors committed by students during level test.

**Task:**

**Individually**, please identify one possible error in each of the error analysis solutions shown below. eg. Conceptual error due to misquoting of (a+b)^2 law. It should be a^2+2ab+b^2 NOT a^+b^2. You may correct part of OR all the errors found in each solution.

In total, you should complete 5 work in all.

__A__

__B__

**C**

**D**

**E**

1.The n should have been multiplied by 5.

ReplyDelete2.The n should not be canceling out each other.

3.The 7 should not negative but positive.

4.(6a+3) when squared is not 36a squared+9.

5.-3y cannot be changed to -9x square

A.The n at the numerator is to be multiplied by 5.

ReplyDeleteB.The m at the numerator cannot be cancelled with the m at the denominator cannot be canceled at the last part.

C.When removing the bracket,the -7 should become +7.

D.It should be -(36a^2+9) then -36a^2-9

E.It should be 9y^2 not 9xy and -3y should not be worked to -9x square

1. The sign is wrong , -x - = + and they did not multiply the n by 5 .

ReplyDelete2.They can not just cancel out the n .

3. The 7 was not multiplied by the 3 and the 7x is positive not negative

4. The ^2 needs to be done first by using the identity then multiplying by the number outside the brackets

5.The expansion for the y outside the bracket is wrong and the expansion for the sign is wrong and the number is wrong ( -3y)

A) Error with the sign conversion (-)(-) = (+). (-)(4m-n/m+n) should be 4 m+n.

ReplyDeleteB) Error in division .Just like using numbers, addition and subtraction can't use this method of canceling. It should eb just 2n+m/m+n.

C) Error in sign conversion. Just like A) (-)(-)=(+) which in this case is (-)(20-7x) which is -20+7x.

D) Error in power sign. The power sign should be taken out first before removing the brackets. It should be in this order -3(2a+1) = -3(4a^2+1)=-12a^2-1

E) Error in multiplication. I should be y(6x-9y) = 6xy-9y^2 not 9xy.

A) There is error with the sign, negative times negative equals positive. So it should be 4m+n. Another problem is that, the n should have been multiplied by 5

ReplyDeleteB) the m cannot be canceled out just like that, it must be a cross multiplication

C) -(20-7x).. before the bracket, there is a 'invisible 1' and when it is multiplied by 1, the signs need to change too because negative times negative equals positive. so it should be, -20+7x

D) The power sign should be done first before multiplying the numbers in the bracket, and the signs are wrong, (-)(+) = (-), it should be -36^2-9

E) it is -(-3y), how can it become 9x^2? Numbers in the question cannot be changed.

1.should be 4m+n, not 4m-n

ReplyDelete2.cancelling cannot be used in addition in the denominator and numerator of the fraction

3.7 must be positive, not negative

4.power sign must be taken out first

5.-3y is not 9x^2

1. It should be 4m+n because if you have 3-(2-1), that would be 3-2+1.

ReplyDelete2. You can not cancel in addition

3. 7(x-3) = 7x - 21 not 7x - 3 and then conversion error. It should be20 + 7x

4. Power sign comes first

5. -3y isn't 9x^2. Y is not X

A) The sign is wrong it should be 4m+n not 4m-n.

ReplyDeleteB)You cannot cancel addition but can cancel when it is multiplication or division.

C)The sign convention is wrong as (-) X (-) = (+) so it should be 7x-3-20+7x

D)The sign convention is again wrong. When there is a negative outside the bracket always remember there is a 1 there thus you have to take note of the sign convention and thus its should be (6a-3)^2

E) It should be 9y^2 and -3y is also not 9y^2

A) <5m+n> The 5 must be also multiplied with the n resulting in 5n.

ReplyDeletethe -n in 4m-n /m+n after it is in one fraction must become +n since - x - = +

B) the m cannot be canceled out since one of them is addition .Cancelation only occurs when both are in multiplication.

C) the result is not 7x -3. the 7 is also multiplied by -3 resulting in -21

and -(20-7x) will result in -+20--70x which will result in = -20+70x

D) < 3(2a+1)^2 > the square belongs to the values in the brackets not including the 3 in multiplication.thus the process of squaring must occur before multiplying with 3.

E) the expression to the right should result in +6xy -9y^2 not +6xy-9xy.

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for (E)

I think it is a (-3y) the whole squared since the brackets will be redundant if they are not in multiplication or other similar processes.

So the correct answer (-3y)^2 will result in (9)(y^2)