Can anyone help me calculate 19 20 questions, hurry up 5

19 solution: 1, from the figure knows, the price of 600 yuan when the sale of 400 pieces, the price of 700 yuan when the sale of 300 pieces, substitute y=kx+b get:

400=600k+b

300=700k+b

So k = -1 and b = 1000. The function formula is y=1000-x

2. (1) From the question: total profit = (sales price - cost price) * sales volume, then s = (x-500) * y = -x 2 + 1500x-500000, and the range of x is [500,800].

2) Organize s into s=-(x-750) 2+62500, obviously the curve of s is a parabola with vertices at (750, 62500) and the opening downward.

Because the value range of x includes the abscissa of the vertex, when the price is 750 yuan, the company can get a maximum gross profit of 62,500 yuan.

20. (1) Solution: The graph is not very clear, what I see is f(x)=a-2 (2 x+1), right?

If so, since f(x) is an odd function defined on r, i.e., f(-x)=-f(x), then.

a-2/(2^(-x)+1)=-a+2/(2^x+1)

Sorted out a=1.

2) Proof: When x is less than 0, 2 x is less than 1, then 2 x+1 is less than 2, that is, 2 (2 x+1) is greater than 1, so y is less than 0;

When x is greater than 0 and 2 x is greater than 1, then 2 x+1 is greater than 2, i.e., 2 (2 x+1) is less than 1, so y is greater than 0.

Hence y is monotonically increasing on r.

19.Solution: 6m=60dm, 3m=30dm

s living room = 60x30 = 1800 (dm).

S floor tile = 3x3 = 9 (dm).

1800 9 = 200 (block).

A: A total of 200 pieces will be used.

20.Solution: s=vt=200x6=1200(m)s=1200x8=9600(m).

A: Able to sprinkle water on the ground of 9600.

19、x+2-4=x^2-2

x^2-x=0

x(x-1)=0

x=0, or x=1

Root test omitted. x=0, or x=1 is the solution of the original equation.

x^2-15x+44=0

x-4)(x-11)=0

x1=4 ,x2=11

x2=11 is not the root of the original number of the backup equation, so the root of the original equation x=4