∫ Point O (0 0,0) and A (4,40) are on this straight line.
∴-40=4k，
The solution is k=- 10,
∴y=- 10x；
Point B is on the parabola, y=-5x2+205x- 1230,
Let B( 10, m), then m = 320.
The coordinate of point B is (10,320).
∵ Point A is the vertex of the parabola, ∴ Let the analytical formula of the parabola where curve AB is located be y=a(x-4)2-40,
∴320=a( 10-4)2-40，
The solution is a= 10,
That is y =10 (x-4) 2-40 =10x2-80x+120.
- 10x(x= 1，2，3，4)
∴y={ 10x^2-80x+ 120(x=5,6,7,8,9)
-50x^2+205x- 1230(x= 10, 1 1, 12)
(2) - 10(x= 1，2，3，4)
S={20x-90(x=5，6，7，8，9)
- 10x+2 10(x = 10， 1 1， 12)
(3) According to (2), when x= 1, 2, 3 and 4, the values of s are all-10.
When x=5, 6, 7, 8, 9, when x=9, the maximum value of s is 90.
And when x= 10,1,12, s=- 10x+2 10,
When x= 10, the maximum value of s is 1 10.
Therefore, the company made the largest profit in the month of 10, which was 165438+ ten thousand yuan.