A circle centered at [tex]$(-1,2)$[/tex] has a diameter of 10 units. Amit wants to determine whether [tex]$(2,-2)$[/tex] is also on the circle. His work is shown below.

The radius is 5 units.

Find the distance from the center to [tex]$(2,-2)$[/tex].
[tex]\[ \sqrt{(-1-2)^2+(2-(-2))^2} \][/tex]
[tex]\[ \sqrt{(-3)^2+(4)^2} = \sqrt{9+16} = \sqrt{25} = 5 \][/tex]

The point [tex]$(2,-2)$[/tex] lies on the circle because the calculated distance is the same as the radius.

Is Amit's work correct?

A. No, he should have used the origin as the center of the circle.
B. No, the radius is 10 units, not 5 units.
C. No, he did not calculate the distance correctly.
D. Yes, the distance from the center to [tex]$(2,-2)$[/tex] is the same as the radius.



Answer :

Let's analyze the problem step by step to determine if Amit's work is correct.

1. Identify the Center and Radius of the Circle:
- The center of the circle is given as [tex]\((-1, 2)\)[/tex].
- The diameter of the circle is 10 units, so the radius [tex]\( r \)[/tex] is half of the diameter:
[tex]\[ r = \frac{10}{2} = 5 \text{ units} \][/tex]

2. Find the Distance from the Center to the Point [tex]\((2, -2)\)[/tex]:
- The coordinates of the given point are [tex]\((2, -2)\)[/tex].
- To find the distance between the center [tex]\((-1, 2)\)[/tex] and the point [tex]\((2, -2)\)[/tex], we use the distance formula:
[tex]\[ \text{Distance} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} \][/tex]
where [tex]\((x_1, y_1)\)[/tex] are the coordinates of the center and [tex]\((x_2, y_2)\)[/tex] are the coordinates of the point.
- Substituting the values:
[tex]\[ \text{Distance} = \sqrt{(2 - (-1))^2 + (-2 - 2)^2} \][/tex]
Simplifying inside the square root:
[tex]\[ \text{Distance} = \sqrt{(2 + 1)^2 + (-2 - 2)^2} = \sqrt{3^2 + (-4)^2} = \sqrt{9 + 16} = \sqrt{25} = 5 \][/tex]

3. Compare the Distance to the Radius:
- The calculated distance from the center to the point [tex]\((2, -2)\)[/tex] is 5 units.
- The radius of the circle is also 5 units.

4. Determine if the Point Lies on the Circle:
- For a point to lie on the circle, the distance from the center to the point must be equal to the radius.
- Since the distance from the center to [tex]\((2, -2)\)[/tex] is 5 units, which is equal to the radius, [tex]\((2, -2)\)[/tex] lies on the circle.

5. Verify Amit's Work:
- Amit stated that the point [tex]\((2, -2)\)[/tex] does not lie on the circle because he calculated the distance incorrectly as 3 units. His steps and conclusion appear flawed.

Hence, Amit's work is incorrect. The correct distance calculation shows that the point [tex]\((2, -2)\)[/tex] lies on the circle. The correct findings are:
- The radius is 5 units.
- The distance from the center [tex]\((-1, 2)\)[/tex] to the point [tex]\((2, -2)\)[/tex] is 5 units.
- Therefore, the point [tex]\((2, -2)\)[/tex] does lie on the circle.