### Home > INT3 > Chapter 12 > Lesson 12.1.3 > Problem12-48

12-48.

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

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

What point on the line $y = 3x$ is $2$ units from the $y$-axis?

Use the coordinates of the center and the radius to write an equation in general form.

$(x - 2)^2 + (y - 6)^2 = 4$

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

See part (a).

$(x - 3)^2 + (y - 9)^2 = 9$

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