Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2007-01-25 17:18:19

jxharmon
Member
Registered: 2007-01-08
Posts: 104

graph inequalities

3x-4y <12 I graphed the points (-4,-6);(4,0); and (0,-3) now I just don't know whether to shade above or below the line???

Offline

#2 2007-01-25 18:41:41

Toast
Real Member
Registered: 2006-10-08
Posts: 1,321

Re: graph inequalities

The shaded region is the region not required. It is where the inequality is not true.

Once you have drawn the graph, use a test coordinate to determine whether you need to shade above or below the line.
Any coordinate can be used, but usually the easiest is the origin, (0,0).

Substitute the coordinates into the inequality:
3(0) - 4(0) < 12
0 < 12
Since the inequation is true, the coordinate (0,0) is part of the required region, and hence shouldn't be shaded. Everything on the OTHER side of the line, however, is not required, and should be shaded.

Note that for inequalities using the sign < and >, the boundary line should be dashed. This is because the boundary line itself is not required.

(If the boundary line goes through the origin, another test coordinate must be used)

Last edited by Toast (2007-01-25 18:42:48)

Offline

Board footer

Powered by FluxBB