Toán A=2^3+2^6+2^9+…..+2^90 B=5^2+5^4+5^6+…..+5^80 Tính nha các bạn 18/09/2021 By Peyton A=2^3+2^6+2^9+…..+2^90 B=5^2+5^4+5^6+…..+5^80 Tính nha các bạn
Bạn tham khảo : $A = 2^3+2^6+2^9+…..+2^{90}$ $8A = 2^6 + 2^9 + 2^12 + … + 2^{93}$ $8A -A =( 2^6 + 2^9 + 2^12 + … + 2^{93}) – (2^3+2^6+2^9+…..+2^{90})$ $7A = 2^93 – 2^3$ $A = \dfrac{2^{93} – 2^3}{7}$ $B = 5^2+5^4+5^6+…..+5^{80}$ $25B = 5^4 + 5^6 + 5^8 + .. + 5^{82}$ $25B – B = (5^4 + 5^6 + 5^8 + .. + 5^{82}) – ( 5^2+5^4+5^6+…..+5^{80})$ $24B = 5^{82} – 5^2$ $B$ =$\dfrac{5^{82} – 5^2 }{24}$ Trả lời
Đáp án: Giải thích các bước giải: \[\begin{array}{l} A = {2^3} + {2^6} + {2^9} + …. + {2^{90}} = 8 + {8^2} + {8^3} + … + {8^{30}}\\ = > 8A = {8^2} + {8^3} + {8^4} + … + {8^{30}} + {8^{31}}\\ = > 7A = {8^{31}} – 8 = > A = \frac{{{8^{31}} – 8}}{7}\\ B = {5^2} + {5^4} + {5^6} + …. + {5^{80}} = 25 + {25^2} + {25^3} + … + {25^{40}}\\ = > 25B = {25^2} + {25^3} + {25^4} + … + {25^{40}} + {25^{41}}\\ = > 24B = {25^{41}} – 25 = > B = \frac{{{{25}^{41}} – 25}}{{24}} \end{array}\] Trả lời
Bạn tham khảo :
$A = 2^3+2^6+2^9+…..+2^{90}$
$8A = 2^6 + 2^9 + 2^12 + … + 2^{93}$
$8A -A =( 2^6 + 2^9 + 2^12 + … + 2^{93}) – (2^3+2^6+2^9+…..+2^{90})$
$7A = 2^93 – 2^3$
$A = \dfrac{2^{93} – 2^3}{7}$
$B = 5^2+5^4+5^6+…..+5^{80}$
$25B = 5^4 + 5^6 + 5^8 + .. + 5^{82}$
$25B – B = (5^4 + 5^6 + 5^8 + .. + 5^{82}) – ( 5^2+5^4+5^6+…..+5^{80})$
$24B = 5^{82} – 5^2$
$B$ =$\dfrac{5^{82} – 5^2 }{24}$
Đáp án:
Giải thích các bước giải:
\[\begin{array}{l}
A = {2^3} + {2^6} + {2^9} + …. + {2^{90}} = 8 + {8^2} + {8^3} + … + {8^{30}}\\
= > 8A = {8^2} + {8^3} + {8^4} + … + {8^{30}} + {8^{31}}\\
= > 7A = {8^{31}} – 8 = > A = \frac{{{8^{31}} – 8}}{7}\\
B = {5^2} + {5^4} + {5^6} + …. + {5^{80}} = 25 + {25^2} + {25^3} + … + {25^{40}}\\
= > 25B = {25^2} + {25^3} + {25^4} + … + {25^{40}} + {25^{41}}\\
= > 24B = {25^{41}} – 25 = > B = \frac{{{{25}^{41}} – 25}}{{24}}
\end{array}\]