Which equation represents a circle that contains the point [tex]$(-2,8)$[/tex] and has a center at [tex]$(4,0)$[/tex]?

Distance formula: [tex]$\sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$[/tex]

A. [tex]$(x-4)^2 + y^2 = 100$[/tex]
B. [tex]$(x-4)^2 + y^2 = 10$[/tex]
C. [tex]$x^2 + (y-4)^2 = 10$[/tex]
D. [tex]$x^2 + (y-4)^2 = 100$[/tex]



Answer :

Let's solve this step-by-step.

We are given a point [tex]\((-2, 8)\)[/tex] and a center [tex]\((4, 0)\)[/tex], and we want to find the equation of the circle that passes through the given point and has the specified center.

### Step 1: Calculate the radius of the circle

To find the radius, we use the distance formula:
[tex]\[ \text{Distance} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} \][/tex]

Here, [tex]\((x_2, y_2) = (-2, 8)\)[/tex] and [tex]\((x_1, y_1) = (4, 0)\)[/tex].

Substitute these values into the distance formula:
[tex]\[ \text{Radius} = \sqrt{(-2 - 4)^2 + (8 - 0)^2} = \sqrt{(-6)^2 + 8^2} = \sqrt{36 + 64} = \sqrt{100} = 10 \][/tex]

So, the radius [tex]\( r \)[/tex] of the circle is 10.

### Step 2: Write the equation of the circle

The general equation of a circle with center [tex]\((h, k)\)[/tex] and radius [tex]\( r \)[/tex] is:
[tex]\[ (x - h)^2 + (y - k)^2 = r^2 \][/tex]

In this case, the center [tex]\((h, k)\)[/tex] is [tex]\((4, 0)\)[/tex] and the radius [tex]\( r \)[/tex] is 10. Plugging these values into the general equation:
[tex]\[ (x - 4)^2 + (y - 0)^2 = 10^2 \][/tex]

Simplified, this becomes:
[tex]\[ (x - 4)^2 + y^2 = 100 \][/tex]

### Step 3: Match the equation with given options

Upon comparison with the provided options:
- [tex]\((x - 4)^2 + y^2 = 100\)[/tex]

We find that this equation matches our derived equation.

Therefore, the correct equation representing the circle that contains the point [tex]\((-2, 8)\)[/tex] and has a center at [tex]\((4, 0)\)[/tex] is:
[tex]\[ (x - 4)^2 + y^2 = 100 \][/tex]