Question

Consider a circle whose equation is x^2 + y^2 – 2x – 8 = 0. Which statements are true? Check all that apply.

A.The radius of the circle is 3 units.
B.The center of the circle lies on the x-axis.
C.The center of the circle lies on the y-axis.
D.The standard form of the equation is (x – 1)² + y² = 3.
E.The radius of this circle is the same as the radius of the circle whose equation is x² + y² = 9.

Answer 1

a c e

Explanation:

Answer 2

Answer: The correct options are

A. The radius of the circle is 3 units.

C. The center of the circle lies on the y-axis.

E. The radius of this circle is the same as the radius of the circle whose equation is x² + y² = 9.

Step-by-step explanation: The given equation of the circle is

`x^2+y^2-2x-8=0~~~~~~~~~~~~~~~~~~~(i)`

We are given to select the TRUE statements from the given options.

The standard form of a circle with radius r units and center (h, k) is given by

`(x-h)^2+(y-k)^2=r^2.`

From equation (i), we have

`x^2+y^2-2x-8=0\\\\\Rightarrow x^2+(y^2-2x+1)-8-1=0\\\\\Rightarrow x^2+(y-1)^2=9\\\\\Rightarrow (x-0)^2+(y-1)^2=3^2.`

comparing the above equation with the standard equation of a circle, we get

center, (h, k) = (0, 1) and radius, r = 3 units.

since the x co-ordinate of the center (0, 1) is 0, so it lies on the Y-axis.

Now, we have

`x^2+y^2=9\\\\\Rightarrow (x-0)^2+(y-0)^2=3^2.`

So, the radius of this circle is 3 units.

That is, the radius of the given circle is same as the radius of the circle whose equation is
`x^2+y^2=9,`

Thus, the standard equation of the given circle is

`x^2+(y-1)^2=3^2,` the center lies on the Y-axis, the radius is 3 units and the radius of the given circle is same as the radius of the circle whose equation is
`x^2+y^2=9.`

Options (A),(C) and (E) are correct.