integrated algebra
posted by sally
how can you solve x^2  3x = 0 i was using a formula as:
x^27x+10=0
(x5)(x+2)= 0
x5=0
x+5 +5 x=5
I was following this formula but got stumped on this question please help.

Damon
x (x3) = 0
x = 0 or x = 3 
sally
before looking at your answer i found the answer to be 0 too but like this:
x^23x=0
x^23x+0=0
(x0)(x+0)=0
0^23(0)=0
was my way right 
Damon
No, because 0x0x is not 3x
You missed the x = 3 root entirely.
Please do it my way :) 
Damon
If you insist on completing the square:
x^2  3x = 0
(3/2)^2 = 9/4
so
x^2  3 x + 9/4 = 9/4
(x3/2)^2 = 9/4 =3/2
x 3/2 = +/ 3/2
x = 3/2 + 3/2 = 3
pr
x = 3/2  3/2 = 0 
Damon
by the way
x^27x+10=0
(x5)(x+2)= 0
x5=0
x = 5
OR
x+2 = 0
x = 2 
sally
do i always have to mention the ors

Damon
If it is a quadratic, in general it has two solutions, so you need to give both.
Sometimes, if the vertex of the parabola is exactly on the x axis, the two roots will be the same. For example:
x^2 4x + 4 = 0
(x2)(x2) = 0
x = 2
or
x = 2 
sally
oh, okay, thank you!
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