Question

If the coordinates of A and B are (-3, a) and (1, a+4) respectively and the mid point of AB is (-1, 1),

Answer 1

$a=-1$

Using the midpoint formula directly from the topic meaning

$\frac{x_{1}+x_{2} }{2} or \frac{y_{1}+y_{2} }{2}$

so

$\frac{a+a+4}{2} =1\\a=-1$