Question

why is the quadratic formula: (-b±sqrt(b^2-4ac))/2a ?

Answer 1

this has been answered so nicely by @myininaya before

Answer 2

they applied completing the square to the quad equation in standard form

Answer 3

I have my own proof but the easier proof is completing the square

Answer 4

:)

Answer 5

This is my proof if you are interested....

Answer 6

\[ax^2+bx+c=0\]
So this is the quadratic equation
This is what the quadratic formula solves

Answer 7

We can do this by completeing the square

Answer 8

http://www.khanacademy.org/math/algebra/quadtratics/v/completing-the-square-to-solve-quadratic-equations

Answer 9

video proof at khanacademy

Answer 10

ooh I get it thank you

Answer 11

is there a formula for cubic or some other polinomial or special function?

Answer 12

yes

solve for x

ax^3+bx^2+c^x+d=0