The Student Room Group

maths gcse factorising help

X Squared - 49


how do u factorise this into brackets
Reply 1
Original post by Sabhani2000
X Squared - 49


how do u factorise this into brackets


(x + 7)(x -7)
Reply 2
Original post by Sabhani2000
X Squared - 49


how do u factorise this into brackets


The difference of two squares :smile:
Reply 3
Original post by Sage25
(x + 7)(x -7)


how did u work that out?
Reply 4
Original post by sage25
the difference of two squares :smile:



thank you!! :smile:
Reply 5
There's no b value (ie a number of x's eg 4x) so you know that it must be difference of two squares because if you expand it out in a square they cancel out eg +7x and -7x. You then just find the square root of c (49) which is 7 and one of them must be negative if its -49
Reply 6
Original post by Sabhani2000
how did u work that out?


The co-efficient of x^2 is 1

so it would be have to be two single x's in the brackets like (x + a)(x + b)

Then, as the number at the end is -49, and there is no value of x it would mean a and b have to multiply to get -49 and add together to get 0

So, 7 x -7 = -49

And

7 + (-7) = 0

Therefore x^2 - 49 = (x + 7) (x - 7)
Reply 7
Original post by sage25
the co-efficient of x^2 is 1

so it would be have to be two single x's in the brackets like (x + a)(x + b)

then, as the number at the end is -49, and there is no value of x it would mean a and b have to multiply to get -49 and add together to get 0

so, 7 x -7 = -49

and

7 + (-7) = 0

therefore x^2 - 49 = (x + 7) (x - 7)


ow ok now i understand !
Thanks for the help! :smile:
Reply 8
Original post by Sabhani2000
ow ok now i understand !
Thanks for the help! :smile:


No problem! :smile:
Reply 9
Unparseable latex formula:

\displaystyle[br]\begin{equation*}a^2 - b^2 = (a+b)(a-b)\end{equation*}

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