Q 17. - Precalculus Enhanced with Graphing Utilities

Question

Write the standard form of the equation and the general form of the equation of each circle of radius $r$ and center $\left(h,k\right)$.

Graph each circle.

$r=4; (h,k)=(-2,1)$

Step-by-Step Solution

Answer

Standard form of the circle is $(x+2{)}^2+(y-1{)}^2=4^2$

General form of the circle is $x^2+y^2+4x-2y-11=0$

Graph is as follows:

Step 1. Given information

It is given that $r=4; (h,k)=(-2,1)$

Step 2. Standard form of the circle

The standard form the circle with center $\left(h,k\right)$ and radius $r$ is $(x-h{)}^2+(y-k{)}^2=r^2$

It is given that $r=4$ and $(h, k)=(-2,1)$.

Therefore, the standard form of the circle is

$\begin{array}{rcl}(x-(-2){)}^2+(y-1{)}^2& =& 4^2\\ (x+2{)}^2+(y-1{)}^2& =& 4^2\end{array}$

Step 3. General form of the circle

The general form of the circle is obtained by simplifying the standard form:

$\begin{array}{rcl}\left(x^2+4x+4\right)+\left(y^2-2y+1\right)& =& 16\\ x^2+y^2+4x-2y+5& =& 16\end{array}$

Subtract $16$ from both sides

$x^2+y^2+4x-2y-11=0$

Step 4. Graph of the circle

Graph is as follows: