You can only cut down a integer number of trees. So you might look at a few integer values for x. As x get large the –x4 term dominates the expression for big losses. x = 0 is easy P(x) = -6. Without cutting any trees you have lost money Put x = 1 and you get for the terms in order -1 + 1 + 7 -1 -6 = 0. So P(x) crosses zero just before you cut the first tree. So you make a profit on only 1 tree. However when x=10 you are back into no profit. So compute a few values for x = 1,2,3,4,5,6,7,8,9.
Y - y1 = m(x - x1)
slope(m) = -3/7
(5,8)...x1 = 5 and y1 = 8
now we sub
y - 8 = -3/7(x - 5) <===
Common ratio can be found by dividing the 2nd term by the first
r = 48/6
r = 8
an = a1 * r^(n-1)
n = term to find = 8
a1 = first number = 6
r = common ratio = 8
now we sub
a(8) = 6 * 8^(8-1)
a(8) = 6 * 8^7
a(8) = 6 * 2097152
a(8) = 12582912 <==
1 and 1/2 is the same as 1.5 and 1.5 * 4 is 6 so I would say 4
