the vlaue of 21C1−10C1+ 21C2−10C2+ 21C3−10C3+ 21C4−10C4+…+ 21C10−10C10is
221−211
221−210
220−29
220−210
21C1−10C1+ 21C2−10C2+ 21C3−10C3+…+ 21C10−10C10 =21C1+21C2+…+21C10− 10C1+10C2+…+10C10 =12 21C1+21C2+…+21C20−210−1=12 21C1+21C2+…+21C21−1−210−1=12221−2−210−1=220−1−210+1=220−210