Question: px+qy+r

Comment on px+qy+r

Hi Brent, for line questions such as these ones, I just wanted to ask for a tip.

Is it safe to assume that the following equation: px+qy+r=0 implies that if it re-arranged as a slope/equation of a formula, it becomes :

px+qy+r=0 --> as an equation of a line --> y= -px/q +r/q

So my question is, will the GMAT test-makers ever try to throw in a trick where "x" in the given equation is actually y value and/or the "y" is actually the "x" value?

Implying that the equation would then become:

px+qy+r=0 --> as an equation of a line --> x= -qy/p + r/p

Thanks!
gmat-admin's picture

Almost!

If a line is defined as px + qy + r = 0, then we can write: y = -px/q - r/q (you have + r/q)

Here, the slope = -p/q and the y-intercept = -r/q

To answer your other question, I've never seen an official GMAT question in which the x-axis and the y-axis are switched. In fact, the term "x-y coordinate plane" assumes that the x-axis is the horizontal axis, and the y-axis the vertical one.

Cheers,
Brent

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