21-25 is -4. Is this helpful?
2,500 subtracted by 372 equals 2148. 2148 dollars is how much savings he has left.
Y = -1/4x + c
5 = -1/4 x 4 + c
5 = -1 + c
c = 6
y = -1/4 + 6
will be increasing on the intervals where
and decreasing wherever
. Local extrema occur when
and the sign of
changes to either side of that point.
is positive when
is between -4 and some number between -2 and -1, and also 2 (exclusive) and 4, so you can estimate that
is increasing on the intervals [-4, -2] and (2, 4].
is negative when
is between some number between -2 and -1, up to some number less than 2. So
is decreasing on the interval [-1, 1].
You then have two possible cases for extrema occurring. The sign of
changes for some
between -2 and -1, and again to either side of
.
