Discrete Math Can you explain the below problem Approximate

Discrete Math: Can you explain the below problem?

Approximate to four decimal places (1.01)^4 (.98)^3 (2.01)^3

Solution

(a)         All the problems are solved using the below formula

              (a+b)ⁿ   = aⁿ + n.a^n-1.b + n(n-1)/2. a^n-2.b² + . . . . . . .

             (1 + 0.01)⁴ = 1 + 10 (0.01) + 45 (0.01)² + 120 (0.01)³

                    = 1+ 0.1+ 0.0045 + 0.00012

                   = 1.10462

(b)     (0.98)³ = (1-0.02)³

                      = 1 - 3(0.02) + 3 (0.02)² - (0.02)³

                      = 1 - 0.06 + 3(0.0004) - 0.000008

                      = 0.941192

(c)     (2.01)³ = ( 2 + 0.01 )³

                      = 8 + 3 . 2². (0.01) + 2 . (0.01)² + (0.01)³

                      = 8 + 0.12 + 0.0006 +0.000001

                       = 8.120601