We've,
(1+x)10=10C0+10C1x+......+ 10C10x10......(1).
Putting x=1 in (1) we get,
210=10C0+10C1+......+ 10C10......(2).
Again putting x=−1 in (1) we get,
0= 10C0−10C1+......+ 10C10......(3).
Now adding (2) and (3) we get,
210=2(10C0+10C2+......+ 10C10)
or, (10C0+10C2+......+ 10C10)=29.