Rút gọn
B = (1 - 1/2 ) . ( 1 - 1/3 ) . ( 1.1/4 ) ... ( 1 - 1/20 )
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NT
2
J
23 tháng 7 2021
B=\(\left(1-\dfrac{1}{2}\right).\left(1-\dfrac{1}{3}\right).\left(1-\dfrac{1}{4}\right)...\left(1-\dfrac{1}{20}\right)\)
\(=\dfrac{1}{2}.\dfrac{2}{3}.\dfrac{3}{4}...\dfrac{19}{20}\)
\(=\dfrac{1.2.3....19}{2.3.4.....20}\)
\(=\dfrac{1.2.3....19:\left(2.3.....19\right)}{2.3.4.....20:\left(2.3.4.....19\right)}\)
\(=\dfrac{1}{20}\)
HN
1
29 tháng 10 2021
\(=3\dfrac{\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)}{8}\)
\(=\dfrac{3\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)}{8}\)
\(=\dfrac{3\left(3^8-1\right)\left(3^8+1\right)\left(3^{16}+1\right)}{8}\)
\(=\dfrac{3\left(3^{16}-1\right)\left(3^{16}+1\right)}{8}\)
\(=\dfrac{3\left(3^{32}-1\right)}{8}\)
37
2
30 tháng 12 2022
uses crt;
var i,s:longint;
begin
clrscr;
s:=1;
for i:=1 to 10 do
s:=s*i;
writeln(s);
readln;
end.
TT
0
AN
1
24 tháng 10 2021
\(A=\dfrac{-4}{9x^2-4}+\dfrac{2x+1}{3x-2}-\dfrac{1}{3x+2}\)
\(=\dfrac{-4+6x^2+4x+3x+2-3x+2}{\left(3x-2\right)\left(3x+2\right)}\)
\(=\dfrac{6x^2+4x}{\left(3x-2\right)\left(3x+2\right)}\)
\(=\dfrac{2x}{3x-2}\)
\(B=\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right)...\left(1-\frac{1}{20}\right)\)
\(B=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{19}{20}\)
\(B=\frac{1.2.3...19}{2.3.4...20}\)
\(B=\frac{1}{20}\)
B=(1-1/2)(1-1/3)........(1-1/20)
B=1/2.2/3.......19/20
B=1/20