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How would you complete the square of these two expressions?

Can someone please walk me through and explain the process of completing the square of these expressions:

1) x^2 + 4x -5

2) x^2 - 20x +10

Thanks!
Original post by blobbybill
Can someone please walk me through and explain the process of completing the square of these expressions:

1) x^2 + 4x -5

2) x^2 - 20x +10

Thanks!


Do you know where to begin? Have you tried anything?
Reply 2
Original post by RDKGames
Do you know where to begin? Have you tried anything?


I know you halve the co-efficient of X and put it in a bracket, then square the bracket, but I don't know how that would work if one of the signs was negative and another was positive (eg the first question)
Original post by blobbybill
I know you halve the co-efficient of X and put it in a bracket, then square the bracket, but I don't know how that would work if one of the signs was negative and another was positive (eg the first question)


In exactly the same way. Remember that 5=+(5)-5 = +(-5) so subtracting a number is the same as adding the negative of it.

So the first one would be just as you said: x2+4x5=x2+4x+(5)=(x+2)2+a+(5)=(x+2)2+a5x^2+4x-5=x^2+4x+(-5)=(x+2)^2+a+(-5)=(x+2)^2+a-5

Can you work out aa and as a result work out the completed square form from there?
(edited 7 years ago)

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