\(A=4^1+4^2+4^3+...+4^{50}\)
\(4A=4^2+4^3+4^4+...+4^{51}\)
\(4A-A=\left(4^2+4^3+4^4+...+4^{51}\right)-\left(4^1+4^2+4^3+...+4^{50}\right)\)
\(3A=4^{51}-4\)
\(A=\frac{4^{51}-4}{3}\)
Đề tự vt đi t giải luôn
\(4A=4^2+4^3+...+4^{51}\)
\(4A-A=\left(4^2+4^3+...+4^{51}\right)-\left(4+4^2+...+4^{50}\right)\)
\(3A=4^{51}-4\)
\(A=\frac{4^{51}-4}{3}\)
\(A=4^1+4^2+4^3+....+4^{50}\)
\(4A=4^2+4^3+4^4+...+4^{51}\)
\(4A-A=\left(4^2+4^3+4^4+...+4^{51}\right)-\)\(\left(4^1+4^2+4^3+...+4^{50}\right)\)
\(3A=4^{51}-4^1\)
\(A=\frac{4^{51}-4}{3}\)
Gọi biểu thức trên là B
B = 4^1 + 4^2 + 4^3 + ... + 4^50
=> 4B = 4^2 + 4^3 + 4^4 + ... + 4^51
4B - B = ( 4^2 + 4^3 + 4^4 + ... + 4^51 ) - ( 4^1 + 4^2 + 4^3 + ... + 4^50 )
=> 3B = 4^51 - 4^1
=> B = 4^51 - 4 / 3
Vậy:
4^1 + 4^2 + 4^3 + ... + 4^5 = = 4^51 - 4 / 3