Math Is Fun Forum

mathland

Member

Registered: 2021-03-25

Posts: 444

Determining Quadrant(s) for a Point

In Exercises 9–14, determine the quadrant(s)
in which (x, y) could be located.

My answers are located below each problem.

9. x > 0 and y < 0

Where is x positive and y negative? Quadrant 4.

10. x < 0 and y < 0

Here, x and y are both negative.  Quadrant 3.

11. x = −4 and y > 0

This is quadrant 2.

12. x < 0 and y = 7

This is quadrant 2.

13. x + y = 0, x ≠ 0, y ≠ 0

I am not too sure about this one. If y = -x, then x - x = 0.
If x = -y, then -y + y = 0.

14. xy > 0

I know that negative times negative is positive.
I also know that positive times positive is positive.
The only quadrant where both x and y are positive is
quadrant 1. This is my answer.

Is any of this right?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,580

Re: Determining Quadrant(s) for a Point

9-12 all ok.

13. Try plotting this as a straight line.  It goes across two quadrants

14. So does this as xy can be positive when both x and y are negative.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mathland

Member

Registered: 2021-03-25

Posts: 444

Re: Determining Quadrant(s) for a Point

9-12 all ok.

13. Try plotting this as a straight line.  It goes across two quadrants

14. So does this as xy can be positive when both x and y are negative.

Bob

Ok. For 13, I say quadrants 1 and 2.

For 14, I say quadrants 1 and 3.

Yes?

Mathegocart

Member

Registered: 2012-04-29

Posts: 2,226

Re: Determining Quadrant(s) for a Point

9-12 all ok.

13. Try plotting this as a straight line.  It goes across two quadrants

14. So does this as xy can be positive when both x and y are negative.

Bob

Ok. For 13, I say quadrants 1 and 2.

For 14, I say quadrants 1 and 3.

Yes?

For 14, yes. Try looking at 13 a little closer.

---

The integral of hope is reality.
May bobbym have a wonderful time in the pearly gates of heaven.
He will be sorely missed.

mathland

Member

Registered: 2021-03-25

Posts: 444

Re: Determining Quadrant(s) for a Point

9-12 all ok.

13. Try plotting this as a straight line.  It goes across two quadrants

14. So does this as xy can be positive when both x and y are negative.

Bob

Ok. For 13, I say quadrants 1 and 2.

For 14, I say quadrants 1 and 3.

Yes?

For 14, yes. Try looking at 13 a little closer.

I don't get 13 at all.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,580

Re: Determining Quadrant(s) for a Point

You have identified the equation as y = -x (correct!) so plot the graph.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mathland

Member

Registered: 2021-03-25

Posts: 444

Re: Determining Quadrant(s) for a Point

You have identified the equation as y = -x (correct!) so plot the graph.

Bob

The graph of y = -x goes through the origin from quadrant 2 down to quadrant 4.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,580

Re: Determining Quadrant(s) for a Point

Excellent!  that's what I needed to see.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mathland

Member

Registered: 2021-03-25

Posts: 444

Re: Determining Quadrant(s) for a Point

Excellent!  that's what I needed to see.

Bob

Thanks.