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Mathematics 23 Online
iosangel:

systems of inequalities

FexrlessRxby:

SS?

AnimeWeeebLMAO:

??

iosangel:

y>−2 x+y≤4

FexrlessRxby:

Do you know what to do first?

iosangel:

plot

FexrlessRxby:

Good good. Then what?

iosangel:

i dont know how to plot y>-2

FexrlessRxby:

Do you know the difference between less than and less than or equal to?

iosangel:

yes

iosangel:

y is greater that -2

FexrlessRxby:

Let me rephrase that. Do you know the difference between the lines?

iosangel:

yes the greater than or equal to? If its greater than or equal to/ less than or equal to it has to be a solid line Right?

FexrlessRxby:

That is correct.

FexrlessRxby:

And what about the normal greater than?

iosangel:

dashed line

FexrlessRxby:

Correct again.

FexrlessRxby:

So y>-2 is a dashed line, we know that so far. Where on the grid would it go?

iosangel:

im not sure

iosangel:

-2 would be the slope?

FexrlessRxby:

That wouldn't be correct because it's not in slope-intercept.

iosangel:

it would be the y intercept?

FexrlessRxby:

Yes. Or in other words, where the line is on the grid.

iosangel:

oh there wouldnt be a slope

FexrlessRxby:

Yes.

iosangel:

so nowi shade the top because > = greater than = top/right side?

FexrlessRxby:

That is correct.

iosangel:

ok thats where i get confused, i have another example where it says y> x-2 but for that i would shade left side, why is that?

FexrlessRxby:

Let me graph that real quick.

FexrlessRxby:

I believe why that is is because there's an "x" in the problem.

FexrlessRxby:

In the original y>-2, there's no "x".

FexrlessRxby:

But in this problem/inequality, there's an "x", so that would cause the shading to switch to the left side.

iosangel:

now im not suere how to graph the second equation

FexrlessRxby:

It would still be the same line, just shaded on the left side instead of the right.

iosangel:

what

iosangel:

4 is the y-intercept in the second equation

iosangel:

im confused?

SmokeyBrown:

|dw:1629828181112:dw| Please excuse my poor drawing skills. As FexrlessRxby was explaining, one way to solve this problem would be to plot the lines (as I tried to do) and then to shade the regions of the graph, based on the sign of the inequality (shade above and to the right for "greater-than"; shade below and to the left for "less-than") The portion where the shading overlaps would be the solution to the system.

iosangel:

And I should shade the same for this x+y≤4

SmokeyBrown:

My mistake, I graphed y >= 2, instead of y > -2, as the question asks (also, the line would be dotted, not solid, for a > sign, as opposed to >=. The drawing still illustrates the idea, even though I got the number wrong. The blue line and shading represents the region y >= 2 and the green line and shading represents the region x+y <= 4

iosangel:

how did u graph x+y≤4

SmokeyBrown:

Apologies, my drawing was not very good. Please refer to this diagram made using Desmos graphing calculator for a clearer picture. x + y ≤ 4 can also be rewritten as y ≤ -x + 4, if that makes it easier to visualize. The graph would be the line y = -x + 4, with shading underneath the line, since the symbol is "≤", signifying "less than", or below the line

1 attachment
iosangel:

where did you get the - in y ≤ -x + 4

SmokeyBrown:

@iosangel wrote:
where did you get the - in y ≤ -x + 4
Good question. You could rewrite the expression y + x ≤ 4 by subtracting x from both sides of the expression: y + x (- x) ≤ 4 (- x) Which gives y + 0 ≤ 4 - x Which is equivalent to y ≤ -x + 4 It is a pretty common operation in algebra, based on the principle that anything done to one side of an expression must also be done to the other side of the expression in order to make it equal. In this case, since we subtract "x" from one side, we have to subtract it from the other side as well; and the result is an expression with equal value and meaning to the original.

iosangel:

oh i forgot about that

iosangel:

but the full question was Which ordered pair is a solution to the system of inequalities? (1, 3) (1, 5) (0, −4) (−2, −3) doesn't that mean which of these options would be in the double shaded region

SmokeyBrown:

That's right, you would want to find out which of the points listed falls within the double-shaded region, meaning it satisfies both of the inequalities in the system

BakugoBasically:

i was learning about this today

iosangel:

so (1,3)

SmokeyBrown:

@iosangel wrote:
so (1,3)
Yup, you got it! This point actually falls on the line on the edge of "y +x ≤ 4"; since it is a solid line (due to the ≤ sign), it counts as within the region. And of course it satisfies the inequality "y > -2" as well. Good job, looks like you did it :)

iosangel:

Thank you

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