Đặt A= 1+3+3^2+3^3+...+3^20
=>3A=3*(1+3+3^2+3^3+...+3^20)
=3+3^2+3^3+3^4+...+3^20
=>3A-A=(3+3^2+3^3+3^4+...+3^21)-(1+3+3^2+3^3+...+3^20)
=>2A=3^21-1
=>A=(3^21-1)/2
Thay vào ta được:(2^31/2)-(3^21-1)/2
=2^30-(3^21-1)/2
cho:
\(A=\frac{1}{2}+\frac{3}{2}+\left(\frac{3}{2}\right)^2+\left(\frac{3}{2}\right)^3+...+\left(\frac{3}{2}\right)^{2012}\)
và \(B=\left(\frac{3}{2}\right)^{2013}\div2\)
tính B - A
Tính:
\(-3^2+\left\{-54:\left[-2^8+7\right]\cdot\left(-2\right)^2\right\}\)
Tính hợp lí :
\(31\cdot\left(-18\right)+31\cdot\left(-81\right)-31\)
\(\left(-12\right)\cdot47+\left(-12\right)\cdot52+\left(-12\right)\)
\(13\cdot\left(23+22\right)-3\cdot\left(17+28\right)\)
\(-48+48\cdot\left(-78\right)+48\cdot\left(-21\right)\)
tìm x
1, \(0,4\cdot x-\frac{1}{5}x=\frac{3}{4}\)
2, \(x\div1\frac{2}{7}=-3,5\)\
3, \(\left(\frac{2x}{5}-2\right)\div\left(-5\right)=\frac{3}{7}\)
4, x+ 20% x = -4,8
5, \(x-15\%x=-2\frac{11}{20}\)
6, \(\left(x\cdot25\%-\frac{2}{3}\right)\div2\frac{1}{3}=1\frac{5}{8}\)
A= \(-1,6\div\left(1+\frac{2}{3}\right)\)
B=\(1,4\times\frac{15}{49}-\left(\frac{4}{5}+\frac{2}{3}\right)\div2\frac{1}{5}\)
\(\left(0,66-0,012\div0,2\right)\div\left(1-1\frac{4}{7}\times0,4\right)=2\frac{9}{13}\times x\div\left(3,125-5,6\div2\frac{2}{3}\right)\)
Cho mình xin cả cách làm nữa
\(A=-5^{22}-\left\{-222-\left[-122-\left(100-5^{22}\right)+2022\right]\right\}\)
\(B=1+\dfrac{1}{2}\left(1+2\right)+\dfrac{1}{3}\left(1+2+3\right)+...+\dfrac{1}{20}\left(1+2+3+...+20\right)\)
\(C=\dfrac{5.4^6.9^4-3^9.\left(-8\right)^4}{4.2^{13}.3^8+2.8^4.\left(-27\right)^3}\)
B=\(1+\dfrac{1}{2}\left(1+2\right)+\dfrac{1}{3}\left(1+2+3\right)+...+\dfrac{1}{20}\left(1+2+3+...+20\right)\)
Tính : \(S=1+\frac{1}{2}\left(1+2\right)+\frac{1}{3}\left(1+2+3\right)+\frac{1}{4}\left(1+2+3+4\right)+...+\frac{1}{20}\left(1+2+3+..+20\right)\)
3.Tính hợp lí:
a,\(\frac{17}{5}.\frac{-31}{125}.\frac{1}{2}.\frac{10}{17}.\frac{-1}{2^3}\)
b,\(\left(\frac{11}{4}.\frac{5}{9}-\frac{4}{9}.\frac{11}{4}\right).\frac{8}{33}\)
c,\(\left(\frac{17}{28}+\frac{18}{29}-\frac{19}{30}-\frac{20}{31}\right).\left(\frac{-5}{12}+\frac{1}{4}+\frac{1}{6}\right)\)
4.Tìm tích:
a,\(\left(\frac{1}{2}+1\right)\left(\frac{1}{3}+1\right).....\left(\frac{1}{99}+1\right)\)
b,\(\left(\frac{1}{2}-1\right)\left(\frac{1}{3}-1\right).....\left(\frac{1}{100}-1\right)\)
c,\(\frac{3}{2^2}.\frac{8}{3^2}.\frac{15}{4^2}....\frac{899}{30^2}\)
AI CÒN THỨC THÌ GIÚP MIK VS,MIK ĐANG CẦN GẤP
