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#1
I'm trying to develop my mathematical understanding

why can't you solve a quadratic such as

x^2+5x+6

by x(X+5)=-6
then
X=-6 and -11 (I know these aren't the real solutions)
0
2 years ago
#2
because if you substitute either of those values for X into X(X+5) you don't get -6
1
#3
so this method can only be used for linear equations?
0
2 years ago
#4
(Original post by utv)
so this method can only be used for linear equations?
What method? Post an example of how you would use this for a linear equation?

To use factorising to solve a quadratic you have to have a zero on one side. Then you know for sure that one of the factors must be zero.
0
2 years ago
#5
factorising can work for quadratics too, but you need to make the equation equal zero first. for example, the equation you mentioned can be factorised to make (x+2)(x+3)=0.
x can be either -2 or -3, because when you substitute either of these values into the equation, one of the brackets will become zero. and as you know, anything multiplied by zero is also.
0
#6
oh ok this makes sense as I was wondering why you couldn't factorise sin theta from sin theta squared -2sin theta +1 .
0
2 years ago
#7
Completing the square, and hence the quadratic formula, is essentially doing something similiar but eliminating the term completely. Therefore, Last edited by SerBronn; 2 years ago
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