QOTD 3/29/2026

For the linear function k, the graph of $y = k(x)$ in the $xy$-plane passes through the points (1, -7) and (7, -25). Which equation defines $k$?

A) $k(x) = -11 + 4x $ B) $k(x) = 3x - 11$ C) $k(x) = -4 - 3x$ D) $k(x) = -3x$

[correct answer: C]

priority level - we all want this one

Quite happily, as is regularly the case, we have options here. Let’s take this opportunity to explore the Plugging in Points(PiP) path toward confidently arriving at our answer.

Using the second of the two points we are given, we could plug in 3 as x into each of the answer options and see which one yields a value of -13. Likely using our calculators for each computation, we can see that only option (C) gives us the -13 we are looking for.

If you are already clued in to PiP and used the technique and selected (A), here are some things to consider….

• i) When executing PiP, it is generally better not to use a point that includes 1 or 0.
• ii) For reasons we won’t get in to right now, given two points that can be used, it often is better to use the second of the two points.
• iii) Regardless of which point you use, you could always make the choice to check all four answer options to be sure that only one option gives you what you are looking for. And, if it does end up that two options yield the same result, you could then test another point to confirm which option is actually our correct answer.

As a final comment, for anyone going a non-PiP route, we’re generally excited about any route that confidently leads you to correct answers.

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