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What is the equation of the circle with center [tex]$(-3.2, 2.1)$[/tex] and radius 4.3?

A. [tex]$(x + 2.1)^2 + (y - 3.2)^2 = 4.3^2$[/tex]
B. [tex][tex]$(x - 2.1)^2 - (y + 3.2)^2 = (4.3)^2$[/tex][/tex]
C. [tex]$(x - 3.2)^2 + (y + 2.1)^2 = (4.3)^2$[/tex]
D. [tex]$(x + 3.2)^2 + (y - 2.1)^2 = 4.3^2$[/tex]


Sagot :

To find the equation of a circle given its center and radius, we use the standard formula for the equation of a circle:

[tex]\[ (x - h)^2 + (y - k)^2 = r^2 \][/tex]

Where:
- [tex]\((h, k)\)[/tex] is the center of the circle
- [tex]\(r\)[/tex] is the radius of the circle

For this specific problem:
- The center of the circle is [tex]\((-3.2, 2.1)\)[/tex], thus [tex]\(h = -3.2\)[/tex] and [tex]\(k = 2.1\)[/tex].
- The radius [tex]\(r\)[/tex] is [tex]\(4.3\)[/tex].

Substituting these values into the standard formula, we get:

[tex]\[ (x - (-3.2))^2 + (y - 2.1)^2 = (4.3)^2 \][/tex]

Simplifying the equation, notice that subtracting a negative number is the same as adding the positive:

[tex]\[ (x + 3.2)^2 + (y - 2.1)^2 = (4.3)^2 \][/tex]

Now, let's compare this derived equation with the given options:

A. [tex]\((x + 2.1)^2 + (y - 3.2)^2 = 4.3^2\)[/tex]
B. [tex]\((x - 2.1)^2 - (y + 3.2)^2 = (4.3)^2\)[/tex]
C. [tex]\((x - 3.2)^2 + (y + 2.1)^2 = (4.3)^2\)[/tex]
D. [tex]\((x + 3.2)^2 + (y - 2.1)^2 = 4.3^2\)[/tex]

Clearly, the correct equation matches option D:

[tex]\[ (x + 3.2)^2 + (y - 2.1)^2 = 4.3^2 \][/tex]

Therefore, the equation of the circle is:

[tex]\[ \boxed{(x + 3.2)^2 + (y - 2.1)^2 = 4.3^2} \][/tex]

The correct answer is option D.