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About Steve Holleran
Expertise
I can help with all math questions from basic math to Calculus. Whether it`s consumer questions, or questions from high school or college students, I have probably dealt with it at some time in my career.

Experience
33 years teaching experience in NJ public schools

Education/Credentials
B.S. Mathematics : Wake Forest University 1972 M.S. Mathematics : Monmouth University 1981

You are here: Experts > Science > Mathematics > Advanced Math > Simultaneous equations

Topic: Advanced Math

Expert: Steve Holleran
Date: 5/28/2008
Subject: Simultaneous equations

Question
I think i have worked out this equation but i dont understand where i have gone wrong please could you help

y=11x+3
y=4x^2

11x+3=4x^2

4x^2-11x+3=0

x=11+ or - squared root (-11)^2-4*4*3/2*4

x= 11 + or - squared root 121-48/8

so x=11+ squared root 73/8=2.44 (to 3 sf)
or
x=11-squared root 73/8=0.31 (to 3sf)

i have tryed plugging in the answers to work out both y's but it doesn't work and i don't understand where i have gone wrong please help me

Answer
Hi Daryl,

Your quadratic formula work is fine, but the trouble is being caused by a sign mistake early on:

                 y = 11x + 3

                 y = 4x^2

so                4x^2 = 11x + 3

and               4x^2 - 11x - 3 = 0 . You had "+3".

This then factors as (4x + 1)(x -3) = 0 so x = -1/4 or 3.

Its usually small things like this that cause complications.
Steve

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