Đáp án:
Đăt A = $2^{50}$ -$2^{48}$ +$2^{46}$ -...-$2^{4}$ +$2^{2}$ -1
=> 4A=$2^{2}$ .A = $2^{2}$ . ( $2^{50}$ -$2^{48}$ +$2^{46}$ -...-$2^{4}$ +$2^{2}$ -1 )
= $2^{52}$ -$2^{50}$ +$2^{48}$ -...-$2^{6}$ +$2^{4}$-$2^{2}$
=> 4A + A =5A = ($2^{52}$ -$2^{50}$ +$2^{48}$ -...-$2^{6}$ +$2^{4}$-$2^{2}$) + ($2^{50}$ -$2^{48}$ +$2^{46}$ -...-$2^{4}$ +$2^{2}$ -1)
=$2^{52}$ - 1
=> A = $\frac{2^{52} - 1}{5}$
