Bạn tham khảo :
$B = 2^2 - 2^4 + 2^6 - 2^4 + .. .+ 2^{98} - 2^{100}$
$4B = 2^4 - 2^6 + 2^8 - 2^10 + ... + 2^{100} - 2^{102}$
$4B + B = ( 2^4 - 2^6 + 2^8 - 2^10 + ... + 2^{100} - 2^{102} ) + ( 2^2 - 2^4 + 2^6 - 2^4 + .. .+ 2^{98} - 2^{100})$
$5B = 2^2 - 2^{102}$
$B = \dfrac{2^2 - 2^{102}}{5}$