JEE Main202331 Jan 2023Morning ShiftMathematicsBinomial TheoremActual
Let α > 0 , be the smallest number such that the expansion of x 2 3 + 2 x 3 30 has a term β x - α , β ∈ N . Then α is equal to _____ .
Correct answer
0
Step-by-step solution
General term of the binomial expansion of x 2 3 + 2 x 3 30 is T r + 1 = C r 30 x 2 / 3 30 - r 2 x 3 r ⇒ T r + 1 = C r 30 · 2 r · x 60 - 11 r 3 So, for term of the form β x - α , we have 60 - 11 r 3 < 0 ⇒ 11 r > 60 ⇒ r > 60 11 ⇒ r = 6 So, T 7 = C 6 30 · 2 6 x - 2 We have also observed β = C 6 30 2 6 is a natural number. ∴ α = 2