Find the equation of the circle incribed in a triangle, if the angle has its sides on the lines:

2x + y - 9 = 0, -2x + y - 1 = 0, and -x + 2y +7 = 0. Draw the figure.

Solving the equations in pairs, you find the vertices to be

(2,5),(5,-1),(-3,-5)

Now you can figure the incenter and inradius of the triangle.

The equation of the circle is then easy.