maths

a = 2 - [1/(1 + b)]

Multiply all terms on the both sides by (1 + b):

a(1 + b) = 2(1 + b) - 1

a + ab = 2 + 2b - 1

a + ab = 1 + 2b

ab - 2b = 1 - a

b(a - 2) = 1 - a

b = (1 - a)/(a - 2)
=

a = 2 - [1 / (1+b)]
a = [2(1+b) - 1] / (1+b)..........右邊通分母
a(1+b) = 2 + 2b - 1
a + ab = 2b + 1
ab - 2b = 1 - a
b(a - 2) = 1 - a
b = (1 - a) / (a - 2)

a = 2-1/1+b

a = 1/1+b

a(1+b) = 1

a+ab = 1

ab = 1-a

b = 1-a/a