(4t)^2+(3t+50)^2=85^2

2. The section should be isosceles trapezoid!

(1) Let the canal depth h, and the equation is:

1/2(h+2+h+0.4)×h = 1.6；

Upper mouth width = h+2; Channel bottom width =h+0.4

(2) Let the number of days be t,

48t= 1.6×750

3.(30+2x)(35-x)= 1200

4. If the selling price is A, then:

(350- 10a)(a-2 1)=400

The solution should add judgment conditions:

A is less than 2 1× 1.2.

Number of pieces =350- 10a.

5. reduce the price by X.

(x/0. 1 * 40+200)(3-2-x)= 200+24

6. we pour x liters,

30-x-(30-x)*x/30= 10/3

7. Find out the functional relationship between sales price and sales volume, and set the following relationship.

X=KY+B, substituting the data in the figure, we can get k=- 1, that is, every time 1 yuan drops, the sales volume will increase 1.

Set the selling price as m,

(m- 120)( 130-m+70)= 1600

8. If the annual interest rate is X, then:

(500 x * 0.8+500-50)( 1+x * 0.8)= 46 1