How do we use the quadratic formula

to understand how to use a quadratic formula we first have to know what is a quadratic formula. the letter in this equation are from the quadratic equation
 ax^2 + bx +c.

Ex://
 x^2+2x-15=0
A= 1
B= 2
C= -15

x= -2+/-√(2^2-4(1)(-15))/2(1)
we will multiply -4(1)(-15) to get 60
we and 2^2+60 and get 64(this is the discriminant)
-2+/-√(64)/2(1)
-2+8/2=3
-2-8/2=5
x = 3,5

if the discriminant is more the 0 then there is more then one solution
if the discriminant is equal to 0 then there is only one solution
if the discriminant is less then 0 then there is no solutions

 
hope this was helpful for more help check these links below:

• http://www.purplemath.com/modules/quadform.htm
• http://paulpietrzak.blogspot.com/2011/01/solving-quadratic-equations-quadratic.html
• http://www.youtube.com/watch?v=LWyXP3lYlpQ