To solve an equation with the quadratic formula
first you have to remember the formula. It's
negative b, plus or minus the square root
of b squared minus four a c, all over two
a. So if my equation is x squared plus three
x minus three equals one. The first thing
I want to do is make sure to set that equal
to zero, so I have to get rid of this one
by subtracting one. Gotta make sure I subtract
one from both sides. I have x squared plus
three x, and then negative three minus one
would be negative four. So my a is the coefficient
of x squared which is one. My b is the coefficient
of x, in this case its three. And c is the
constant, negative four. SO I'm going to plug
in my one, three, and negative four into my
quadratic formula. So negative b would be
negative three, plus or minus. B squared would
be three squared, minus four times a which
is one, c is negative four, all over two times
a, which is one. Now I'm going to figure out
what goes in that square root, so I do three
squared minus four times one times negative
four. I get twenty five. So I can rewrite
this as negative three, plus or minus the
square root of twenty five over two times
one is two. Then I can figure out that this,
square root of twenty five is five. I can
use my calculator if I'm not sure. So I can
rewrite this as negative three, plus or minus
five, over two. And then I'm just going to
do two solutions. Negative three plus five
over two and negative three minus five over
two. If I do negative three plus five, I get
two. Over two. Two divided by two is one.
If I do negative three minus five, I get negative
eight. Over two. Negative eight divided by
two is negative four. So my answers are x
equals one and negative four
