1)  a4 =  1.8, a7 = 0.6

a1 - ?, d - ?

d = (a7 - a4)/(7 - 4) = -0.4

a1 = a4 - 3d = 3

2)b2 = -2, b4 = -6

b4 = b2 * q^2

q^2 = 3

1 случай:

q = sqrt(3)

b7 = b2*q^5

b7 = -2 * 9sqrt(3) = -18sqrt(3)

2 случай:

q = -sqrt(3)

b7 = b2*q^5

b7 = -2 * (-9sqrt(3)) = 18sqrt(3)