Question

The number of distinct terms in expansion of $\left( x^{2} + \frac{1}{x^{2}} + 5 \right)^{15}$is–

• A. 256
• B. 60
• C. 31
• D. 61

Answer 1

Answer: (C)

31

Answer 2

Expansion $\frac{(1 + 5x^{2} + x^{4})^{15}}{x^{30}}$

Ž Let x² = t ; $\frac{(1 + 5t + t^{2})^{15}}{t^{15}}$

\ No. of terms = (15 × 2) + 1 = 31 terms.