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Q&A #202

Teachers' Lounge Discussion: Graphing linear inequalities

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From: Bobby Hostler <hostlerb@yahoo.com>
To: Teacher2Teacher Public Discussion
Date: 2007071611:38:04
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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