Question

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

Answer 1

Your answers are B and E

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.