Textbook Problem

Find the midpoint of the line segment that joins each pair of points:

a) $\left(-3,-7\right)$ and $\left(\mathrm{2,\; 5}\right)$	c) $\left(-a,-b\right)$ and $\left(a,b\right)$
b) $\left(\mathrm{0,\; 0}\right)$ and $\left(-\mathrm{2,\; 6}\right)$	d) $\left(2a,2b\right)$ and $\left(2c,2d\right)$