Friday, November 3, 2006

The Quadratic Formula

What's going on in math these days? I asked.

Oh, quadratic equations, he said. You know, b squared minus 4 a c.

You mean the quadratic formula? I asked.

Yes.

So I had him explain it. And we went thru the derivation, which he got mostly right. And I showed him what it meant graphically. And then I told him what I used to ask on exams.

I told him how I promised my students that they would have to derive the quadratic formula on the test. And I told him how when I wrote the tests, I would tell them that instead of starting from

ax2 + bx + c = 0

that they should derive the formula using different coefficients:

Dx2 + Ex + F = 0.

His eyes widened. And then I pointed out that it that it could be worse: I could have used α/β/γ as the coefficients and ξ as the unknown instead of x.

A few minutes later, him mom arrived. As he got into the car I said, Practice the derivation tonite with D/E/F, and you'll never have any trouble with it.

Or with ξ! he said.

What do you think are the odds that he did it?


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