Well, if it is increasing at a fixed rate of 2 mm/s, then the volume would still be increasing at a rate of 2 mm/s when the diameter is 80 mm, if I understand your question correctly.
Answer:
x=75
Step-by-step explanation:
We can use proportions to solve this problem. Put the side of the small triangle over the side of the large triangle.
42 50
------ = ----------
42+63 50+x
42 50
------ = ----------
105 50+x
Using cross products
42(50+x) = 50*(105)
2100+42x = 5250
Subtract 2100 from each side
2100-2100+42x = 5250-2100
42x =3150
Divide by 42
42x/42 = 3150/42
x = 75
Answer and workings in the attachment below. Also, do me one big favour. Let me know if it's the answer your teacher or text book ends up giving you. That would give me some satisfaction.
Answer: 80%
The x coordinate of the vertex will be the average of the two zeros, here -3 and 5, so x=(-3+5)/2 = 1, f(1)=(1+3)(1-5) = -16.
Answer: (1, -16)
Let's do it some other ways. How about completing the square to turn f in to vertex form?
f(x) = (x+3)(x-5) = x² - 2x - 15 = (x² - 2x + 1) - 1 - 15 = (x-1)² - 16
and now we can read off (1, -16) as the vertex.
The other method is the vertex is x= - b/2a = - (-2)/2(1) = 1.
Three methods, same answer. Good.