Question

If the point (1,5) lies on a circle with center (0,0), determine which point in quadrant 2 that also lies on the circle.

Answer 1

Explanation:

since the center of the circle is at the origin, that means that the circle is evenly going through all four quadrants - one quarter arc after the other.

the point (1, 5) is in the first quadrant (upper right one, positive x, positive y).

the circle arc in the second quadrant (upper left one, negative x, positive y) is the mirrored image of the arc in the first quadrant across the y-axis.

so, the point on it gets mirrored too.

that means, it's coordinates are then the same y and the x is converted to its negative value :

(-1, 5)

that is the easily identifiable point in the second quadrant that has to be on the circle.

Answer 2

If the point (1,5) lies on a circle with center (0,0), then the radius of the circle is the distance from the center to the point (1,5), which is:

r = sqrt((1-0)^2 + (5-0)^2) = sqrt(26)

So the equation of the circle is:

x^2 + y^2 = 26

To find a point in quadrant 2 that lies on the circle, we need to find a point with a negative x-coordinate and a positive y-coordinate that satisfies this equation.

Among the given options, only (a) (-5,1) and (e) (-2,3) have a negative x-coordinate. Let's check if they satisfy the equation of the circle:

For point (a) (-5,1):

x^2 + y^2 = 26

(-5)^2 + 1^2 = 26

25 + 1 = 26

This point does not lie on the circle.

For point (e) (-2,3):

x^2 + y^2 = 26

(-2)^2 + 3^2 = 26

4 + 9 = 26

This point also does not lie on the circle.

Therefore, among the given options, there is no point in quadrant 2 that lies on the circle.