Math Is Fun Forum

planetdomi

Member

Registered: 2011-09-17

Posts: 16

Quadratics

Using the quadratic formula why does

y² + y + 1 = 0

equal a negative answer ??

Bob

Administrator

Registered: 2010-06-20

Posts: 10,626

Re: Quadratics

hi planetdomi

Have you met the 'quadratic formula'?

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

planetdomi

Member

Registered: 2011-09-17

Posts: 16

Re: Quadratics

Yes I have substituted into the quadratic formula but I only get a positive answer and my workbook suggests
that b2-4ac is negative. I just cant see it

Bob

Administrator

Registered: 2010-06-20

Posts: 10,626

Re: Quadratics

Yes, it is negative, and that means it cannot be solved with real numbers.  I've used the MIF function grapher to show what it looks like.  I've had to use 'x' instead of 'y' for the across variable but that doesn't alter the equation.

I'll just substitute into the quadratic formula and post that next.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Bob

Administrator

Registered: 2010-06-20

Posts: 10,626

Re: Quadratics

Quadratic formula.

In this case a = 1;   b = 1; and c = 1;  so

Bob

Last edited by Bob (2011-09-24 20:35:18)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

planetdomi

Member

Registered: 2011-09-17

Posts: 16

Re: Quadratics

Sorry for the delay in posting been away from my desk.
Thankyou very much it helps a lot