Verified answer

напомню область значений функций

E(sin) = [-1, 1]

E(cos) = [-1,1]

E(arccos) = [0, π]

E(arcctg) = (0, π)

1. cos x/2 = a

-1 ≤ a ≤ 1

значение A a∈[-1, 1]

2. 1/π arcctg x = a

arcctg x = πa

0 < πa <  π

0 < a < 1

значение Д a∈(0, 1)

3. 1/2 sin 2x = a

sin 2x = 2a

-1 ≤ 2a ≤ 1

-1/2 ≤ a ≤ 1/2

значение Б a∈[-1/2, 1/2]

4. 1/π arccos x = a

arccos x = πa

0 ≤ πa ≤ π

0 ≤ a  ≤ 1

Значение Г a∈[0, 1]