Teacher2Teacher Q&A #202

Teachers' Lounge Discussion: Graphing linear inequalities

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From: Bobby Hostler

To: Teacher2Teacher Public Discussion
Date: 2007071612:38:04
Subject: Re: discriminants and roots?

Why does a quadratic equation have one soution if the discriminant is zero. I don't know how to explain that. Ans: if the Discriminant is zero the function only crosses the x axis at one location therefore the discriminant is 1. easiest example would be y=x^2 versus y=x^2-9 on graphing calculator. What does a parabola with 2 x-intercepts look like in equation form? Ans: there are many solutions to this question but the easiest is probably y=x^2-b were b is constant. this will chose the vertex to move below the x-axis. again look at the examples above on your graphing calculator. For which value of k does kx2 - 10x + 25k = 0 -1, 2, 3, 5 or 10? Ans: Use the discriminant to help you with this one. as long as the solution is a real number (not a complex number or b^2-4ac < 0) it will work. by the way this is asking you for what values of k does the graph cross the x-axis. so using an graphing calculator and substituting the numbers in for k may be easier.

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