\(B=2+2^2+2^3+...+2^{203}\)
\(2B=2^2+2^3+2^4+...+2^{204}\)
\(2B-B=\left(2^2+2^3+2^4+...+2^{204}\right)-\left(2+2^2+2^3+...+2^{203}\right)\)
\(B=2^{204}-2\)
Câu C mk nghĩ là thế này
\(C=1+3+3^2+...+3^{101}\)
\(3C=3+3^2+3^3+...+3^{102}\)
\(3C-C=\left(3+3^2+3^3+...+3^{102}\right)-\left(1+3+3^2+...+3^{101}\right)\)
\(2C=3^{102}-1\)
\(C=\frac{3^{102}-1}{2}\)