Andrew is writing a coordinate proof to show that the triangle formed by connecting the midpoints of the sides of an isosceles triangle is itself an isosceles triangle. He starts by assigning coordinates as given. Fill in the blanks
P is the midpoint of lineDE. Therefore, the coordinates of P are (___,b


Q is the midpoint of lineDF. Therefore, the coordinates of Q are (3a,__).

R is the midpoint of lineEF. Therefore, the coordinates of R are (__, __)

The length of linePR is √​​a2+b2​ . The length of lineQR is √​a2+b2.

Comparing the expressions for the lengths of line PR and lineQR shows that the lengths are equal. Therefore, △PQR is isosceles.