Question

please help? Will give medal to the person who explains his to me.
Use the quadratic formula to solve the equation. –x2 + 7x = 8

Answer 1

A Quadratic Equation\[ax^2+bx+c=0\]
The Quadratic Formula\[\displaystyle\boxed{x_{1,2}=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}}\]
Start by rearranging the equation into the form:
\[ax^2+bx+c=0\]
Then find the coefficients \(a\),\(b\),\(c\).

Answer 2

so right now i have
-1x^2+7x+?=8

Answer 3

that's a good start, but you need to get `= 0` on the right hand side,
so take away 8 from both sides of the equation...

Answer 4

-1x^2+7x-8=0 is this right?

Answer 5

Yes, so what are the coefficients?

Answer 6

-1 and 7?

Answer 7

yeah a = -1
and b =7
but what is c =

Answer 8

-8 but i thought a coefficient needed a variable so i didnt include it

Answer 9

oh, um, yeah ok, i guess c isn't really a coefficient, but, yes c =-8

Answer 10

Now just sub these;
\[a =-1, \qquad b=7, \qquad c=-8\]into the Quadratic formula
\[\displaystyle\boxed{x_{1,2}=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}}\]

Answer 11

if you want to take it slow, you could work out
\[\sqrt{b^2-4ac}\] first

Answer 12

ok i did that and have 17 under the square root symbol

Answer 13

very good,
notice that 17 is prime, so the square root of it will not simply, i.e your final answers will have \(\sqrt{17}\) terms in them

Answer 14

now sub in \(a\) and \(b\) into
\[x_{1,2}=\dfrac{-b\pm\sqrt{17}}{2a}\]