Endpoints of diameter: (6, -2) and (10, -10)

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

Suppose a gym membership has an initial enrollment fee of $75 and then a fee of $29 a month. which equation models the cost, c, of the gym membership for m months?