Marissa's answer to Ria's Secondary 3 E Maths Singapore question.
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Hi Ria, there are some errors in your workings. Otherwise, your answer would match your teacher's.
Date Posted:
5 years ago
Hi thank you so much for your help but I still don’t get it for the cross multiplication 3×y=3y and -2y×5=-10y and 3y plus -10y is equal to -7y in the cross multiplication! No I don’t get why we have to have a negative sign on both numbers 3 and 5 in the cross multiplication? Will you please explain to me thank you so much
Hi, while doing this cross multiplication the last row must be the same as your equation. As you can see, from your working, your end equation is 2y^2+15-7y but the equation you have written at the beginning is -2y^2+15y-7y. So there is a need for a negative sign on either 2y or y.
For your question on why we have to put -3 and -5, after putting the negative sign on y in the first column, you realise that the only way you can get -7y in the last row and last column is by putting -3 and -5.
It can only be both positive or both negative. In this case, it cannot be both positive as you will not get the -7y in the end.
Hope this answers your question.
For your question on why we have to put -3 and -5, after putting the negative sign on y in the first column, you realise that the only way you can get -7y in the last row and last column is by putting -3 and -5.
It can only be both positive or both negative. In this case, it cannot be both positive as you will not get the -7y in the end.
Hope this answers your question.
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