Comments on: How do I do this middle school math function question?

By: SG

SG — Sat, 06 Feb 2010 12:07:59 +0000

since x increses by 2, then the y will increase by 6
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By: Dave B.

Dave B. — Sat, 06 Feb 2010 11:35:59 +0000

Take a look at your table:

When x increases from -1 to 1, y increases from -8 to -2. That’s an increase of 6.

When x increases from 0 to 2, y increases from -5 to 1. That’s also an increase of 6.

You don’t have to know the equation. All you have to do is look at the data. The data tells you it increases by 6.
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By: michaelempeigne

michaelempeigne — Sat, 06 Feb 2010 11:02:59 +0000

y = 3x – 5

when x is increased by 2:
y = 3(x + 2) – 5
y = 3x + 6 – 5
y = 3x + 1

(3x +1) – (3x – 5)
= 3x + 1 – 3x + 5
= 6

That’s too long and tedious, here’s a short way:
dy / dx = 3
dy = 3 dx
dy = 3(2)
dy = 6

the fact that it’s positive indicates that it’s increasing, therefore y increases by 6.
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By: Juan N

Juan N — Sat, 06 Feb 2010 10:42:59 +0000

compare the y values when x changes from 0 (as in the pair (0,-5)) to 2 (as in the pair (2,1) when x increases by 2 (from 0 to 2), the y value increases from (-1) to 5: A difference of 6 in the positive direction.
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