CBSE Class 10 Answered

X = 3+3^2/3+3^1/3

This series is a GP 3^1/3 + 3^2/3 + 3^3/3

First Term = 3^1/3

Common ratio = 3^1/3

Sum = X = 3^1/3 + 3^2/3 + 3^3/3

                 = 3^1/3 ((3^1/3)³ - 1)/ (3^1/3 - 1))

                 = 3^1/3 (2)/ (3^1/3 - 1)

                 = 2 . 3^1/3/ (3^1/3 - 1)

Substituting the value of 3^1/3 , we get the value of X = 6.5

Now to compute the value of expression X³ -9X ² +18X -12 substitute X = 6.5

X³ -9X ² +18X -12 = (6.5)³ -9(6.5) ² +18(6.5) -12

                                 = -0.625