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NDA 2025 Maths · Mathematics · Binomial Theorem · easy

The number of terms in the expansion of (x+y)^10+(x-y)^10 after simplification is

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The number of terms in the expansion of (x+y)10+(x−y)10(x+y)^{10}+(x-y)^{10} after simplification is
  1. A. 1111
  2. B. 55
  3. C. 66
  4. D. 1010
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Answer: (C) 66

Terms with odd powers of yy cancel and those with even powers double: 2[x10+(102)x8y2+⋯+y10]2\left[x^{10}+\binom{10}{2}x^8y^2+\dots+y^{10}\right]. The powers of yy are 0,2,4,6,8,100,2,4,6,8,10, giving 66 terms. The value 1111 ignores the cancellation.
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