# Find the Equation of the Circle Concentric with the Circle X2 + Y2 − 6x + 12y + 15 = 0 and Double of Its Area. - Mathematics

Find the equation of the circle concentric with the circle x2 + y2 − 6x + 12y + 15 = 0 and double of its area.

#### Solution

Let the equation of the required circle be

$x^2 + y^2 + 2gx + 2fy + c = 0$

The centre of the circle x2 + y2 − 6x + 12y + 15 = 0 is (3, −6).

Area of the required circle = $2\pi r^2$

Here, r = radius of the given circle

Now, r = $\sqrt{9 + 36 - 15} = \sqrt{30}$

∴ Area of the required circle = $2\pi\left( 30 \right) = 60\pi$

Let R be the radius of the required circle.

∴$60\pi = \pi R^2 \Rightarrow R^2 = 60$

Thus, the equation of the required circle is

$\left( x - 3 \right)^2 + \left( y + 6 \right)^2 = 60$
$x^2 + y^2 - 6x + 12y = 15$
Concept: Circle - Standard Equation of a Circle
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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 24 The circle
Exercise 24.2 | Q 11 | Page 32