Only a10 (x+1)10 in the expansion on the right side of the original equation contains x^ 10/0. By comparison, the left side can know that:

a 10= 1

Moreover, because the left side does not contain the x 9 term, the sum of all the coefficients containing the x 9 term on the right side is 0.

So obviously, only A9 (x+ 1) 9, a10 (x+1)10 contain x 9.

According to binomial theorem:

a9+ 10×a 10=0

So:

a9 = - 10