The area formula of trapezoid is s = 2 / (a + b) H. if the lower base B = 25, height h = 12 and area s = 240 are known, the value of upper base a can be obtained

The area formula of trapezoid is s = 2 / (a + b) H. if the lower base B = 25, height h = 12 and area s = 240 are known, the value of upper base a can be obtained

Let the top and bottom be a
（a+25）*12/2=240
6a+150=240
a=15

The known trapezoid area formula is s = [a + b] h △ 2
1. Change the above formula into a formula for s, a, B and H;
2. If a: B: S = 2:3:4, find the value of H

1、h=2s÷（a+b）2、s=2a,b=1.5ah=2s÷（a+b）=2×2a÷（a+1.5a）=4a÷2.5a=1.6

If s, h, a are known, then B can be expressed as ()

b=S/hx1/2-a