### Home > A2C > Chapter 9 > Lesson 9.1.2 > Problem9-44

9-44.

A circle with its center on the line $y = 3x$ in the 1st quadrant is tangent to the y-axis.

1. If the radius is $2$, what is the equation of the circle?

Try sketching the circle. The circle to the right has a radius of 2. Try placing it on the axis so it matches the circle described in the problem. The line y = 3x has been graphed for you.

Use the coordinates of the center and the radius to write an equation in general form.
$\left(x − 2\right)^{2} + \left(y − 6\right)^{2} = 4$

2. If the radius is $3$, what is the equation of the circle?

See part (a).

$\left(x − 3\right)^{2} + \left(y − 9\right)^{2} = 9$

Use the eTool below to explore the problem further.
Click the link at right for the full version of the eTool: 9-44 HW eTool