Большее основание=х, меньшее=у.
![\left \{ {{x:y=7:3} \atop {x-y=3.2}} \right.](https://tex.z-dn.net/?f=%5Cleft+%5C%7B+%7B%7Bx%3Ay%3D7%3A3%7D+%5Catop+%7Bx-y%3D3.2%7D%7D+%5Cright.)
![\left \{ {{x=3.2+y} \atop {(3.2+y):y=7:3}} \right.](https://tex.z-dn.net/?f=%5Cleft+%5C%7B+%7B%7Bx%3D3.2%2By%7D+%5Catop+%7B%283.2%2By%29%3Ay%3D7%3A3%7D%7D+%5Cright.)
Решим второе уравнение системы. По пропорции:
7y=3(3.2+y)
7y=9.6+3y
4y=9.6
y=2.4
x=3.2+y=3.2+2.4=5.6
Средняя линия равне полусумме оснований трапеции:
L=(2.4+5.6)/2=8/2=4
Ответ: 4
A₁₁ = a₁ + 10d
10d = a₁₁ - a₁ = 46 - 6 = 40
d = 40 : 10 = 4
a₁₂ = a₁ + 11d = 6 + 11 * 4 = 6 + 44 = 50
![S _{12} = \frac{a _{1}+a _{12} }{2} *12= \frac{6+50}{2}*12=56*6=336](https://tex.z-dn.net/?f=S+_%7B12%7D+%3D+%5Cfrac%7Ba+_%7B1%7D%2Ba+_%7B12%7D++%7D%7B2%7D+%2A12%3D+%5Cfrac%7B6%2B50%7D%7B2%7D%2A12%3D56%2A6%3D336+)
4^x>=1/2
2^2x>=2^(-1)
2x>=-1
x>=(-1/2)
x=[-0,5; беск.]
ответ А