# If x1+x2=-b/a and x1*x2=c/a: how can i do x1-x2

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### 1 Answer

We have `x_1+x_2=-b/a` and `x_1*x_2=c/a`

`(x_1-x_2)` have to be found out.

we know, `(x_1-x_2)^2`

=`x_1^2-2*x_1*x_2+x_2^2 `

= `(x_1+x_2)^2-4*x_1*x_2` [as `(x_1+x_2)^2=x_1^2+2*x_1*x_2+x_2^2` ]

Putting the values of `(x_1-x_2)` and `x_1*x_2` we get,

`(x_1-x_2)^2=(-b/a)^2-4*c/a`

= `b^2/a^2-4c/a`

=`(b^2-4*a*c)/a^2`

`(x_1-x_2) = +-sqrt(b^2-4*a*c)/a`

**=>answer**