So Sánh:
A=\(\frac{7^{100}-5}{7^{100}-2025}\) B=\(\frac{7^{100}-2025}{7^{100}-2045}\)
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\(\left(\frac{75}{100}-\frac{60}{100}+\frac{3}{7}+\frac{3}{11}\right)+\left(\frac{275}{100}-\frac{220}{100}+\frac{11}{7}+\frac{11}{13}\right)\)\(=\frac{1311}{1540}+5\frac{331}{420}\)\(=6\frac{211}{330}\)
HỌC TỐT!!!
\(\left(\frac{75}{100}-\frac{60}{100}+\frac{3}{7}+\frac{3}{11}\right)+\left(\frac{275}{100}-\frac{220}{100}+\frac{11}{7}+\frac{11}{13}\right)\)
\(=\frac{3}{20}+\frac{3}{7}+\frac{3}{11}+\frac{11}{20}+\frac{11}{7}+\frac{11}{13}\)
\(=\frac{14}{20}+\frac{14}{7}+\frac{160}{143}=\frac{3231}{715}+\frac{14}{7}=\frac{4661}{715}\)
Đặt \(E=\frac{1}{7}+\frac{1}{7^2}+\frac{1}{7^3}+...+\frac{1}{7^{99}}+\frac{1}{7^{100}}\)
\(\Rightarrow7E=1+\frac{1}{7}+\frac{1}{7^2}+...+\frac{1}{7^{98}}+\frac{1}{7^{99}}\)
\(\Rightarrow7E-E=\left(1+\frac{1}{7}+...+\frac{1}{7^{98}}+\frac{1}{7^{99}}\right)-\left(\frac{1}{7}+\frac{1}{7^2}+...+\frac{1}{7^{99}}+\frac{1}{7^{100}}\right)\)
\(\Rightarrow6E=1-\frac{1}{7^{100}}\)
\(\Rightarrow E=\frac{1-\frac{1}{7^{100}}}{6}\)
\(\Rightarrow A=\left(36-\frac{36}{7^{100}}\right):\frac{1-\frac{1}{7^{100}}}{6}\)
\(\Rightarrow A=36\left(1-\frac{1}{7^{100}}\right).\frac{6}{1-\frac{1}{7^{100}}}\)
\(\Rightarrow A=36.6=216\)
Đăt A = \(\frac{1}{7}+\frac{1}{7^2}+\frac{1}{7^3}+......+\frac{1}{7^{100}}\)
\(\Rightarrow7A=1+\frac{1}{7}+\frac{1}{7^2}+.....+\frac{1}{7^{100}}\)
\(\Rightarrow7A-A=1-\frac{1}{7^{100}}\)
\(\Rightarrow6A=1-\frac{1}{7^{100}}\)
\(\Rightarrow A=\frac{1-\frac{1}{7^{100}}}{6}\)
a,1+1+2+2+3+3+...+100+100
=1x2+2x2+3x2+...+100x2
=2x(1+2+3+...+100)
=\(2.\frac{\left(100+1\right).\left[\left(100-1\right):1+1\right]}{2}\)
=2x5050
=10100
Chú ý dấu . là x
a, 1+1+2+2+3+...+100+100
=1+2+3+...+100+1+2+3+...+100
= (100+1)*50 /2 + (100+1)*50/2
=5050+5050
=11000
2 x A = 1 - \(\dfrac{1}{2027}\)
\(A=\dfrac{1013}{2027}\)