因为a,b互为相反数,
所以a + b = 0
a + 2a + …… + 99a + 100a + b + 2b +……+ 100b
= (a + b) + (2a + 2b) + ...+ (99a + 99b) + (100a + 100b)
= 0 + 0 + ...+ 0 + 0
= 0