Binomial Theorem
Properties of Binomial Expansion
Premium Question
Grade 11
Question:
If the $2^{\text{nd}}, 3^{\text{rd}}$ and $4^{\text{th}}$ terms in the expansion of $(a + b)^n$ are $240, 720$ and $1080$ respectively, then $n$ equals:
(1) $5$
(2) $6$
(3) $4$
(4) $7$
Step-by-Step Solution
Key Concept: Form the ratios $\frac{T_3}{T_2}$ and $\frac{T_4}{T_3}$ in terms of $n, a, b$ — these ratios will let you eliminate $\frac{b}{a}$ and obtain a single equation in $n$ alone.
The detailed step-by-step mathematical proof is available inside the Mathbee app workspace.
Correct Answer: (1)