Problem: The sum of the numerical coefficients in the complete expansion of (x2−2xy+y2)7 is:
Answer Choices:
A. 0
B. 7
C. 14
D. 128
E. 1282
Solution:
(x2−2xy+y2)7=((x−y)2)7=(x−y)14. By setting x=y=1 in the expansion of this binomial we obtain the sum s of the integer coefficients. Consequently s=(1−1)14= zero