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Ta có:
\(\dfrac{637.527-189}{526.637+448}=\dfrac{637.\left(526+1\right)-189}{526.637+448}=\dfrac{637.526+637-189}{526.637+448}=\dfrac{637.526+448}{526.637+448}=1\)
(637.527-189):(526.637+448)
= \(\frac{637.527-189}{526.637+448}\)
= \(\frac{637.\left(526+1\right)-189}{526.637+448}\)
= \(\frac{637.526+637-189}{526.637+448}\)
= \(\frac{637.526+448}{526.637+448}\)
= \(1\)
\(a)\)\(\left(1989.1990+3978\right)\div\left(1992.1991-3984\right)\)
\(=\)\(\left(1989.1990+1989.2\right)\div\left(1992.1991-1992.2\right)\)
\(=\)\(\left[1989.\left(1990+2\right)\right]\div\left[1992.\left(1991-2\right)\right]\)
\(=\)\(\left(1989.1991\right)\div\left(1992.1989\right)\)
\(=\)\(1\)
\(b)\)\(\left(637.527-189\right)\div\left(526.637+448\right)\)
\(=\)\(\left[637.\left(526-1\right)-189\right]\div\left(526.637-448\right)\)
\(=\)\(\left[637.526+\left(637-198\right)\right]\div\left(637.526-448\right)\)
\(=\)\(\left(636.526+448\right)\div\left(637.526-448\right)\)
\(=\)\(1\)
a)=\(\frac{637x\left(526+1\right)-189}{526x637+448}\)
=\(\frac{637x526+637-189}{526x637+448}\)
=\(\frac{637x526+448}{526x637+448}\)
=\(1\)(vì tử số =mẫu số)
b)=\(\frac{\left(134+1\right)x269-133}{134x269+136}\)
=\(\frac{134x269+269-133}{134x269+136}\)
=\(\frac{134x269+136}{134x269+136}\)
=1(vì tử số =mẫu số)
\(=\dfrac{637.\left(526+1\right)-189}{526.637+448}=\dfrac{637.526+637-189}{526.637+446}=\dfrac{637.526+448}{526.637+448}=1\)
\(\left(637.527-189\right):\left(526.637+448\right)\)
\(=\left(335699-189\right):\left(335062+448\right)\)
\(=335510:335510\)
\(=1\)
\(\frac{19}{37}+\left(1-\frac{19}{37}\right)\)
\(=\frac{19}{37}+1-\frac{19}{37}\)
\(=\left(\frac{19}{37}-\frac{19}{37}\right)+1\)
\(=0+1=1\)
\(C=\dfrac{1}{3\cdot5}+\dfrac{1}{5\cdot7}+...+\dfrac{1}{37\cdot39}\)
\(2C=\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+...+\dfrac{2}{37\cdot39}\)
\(2C=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{37}-\dfrac{1}{39}\)
\(2C=\dfrac{1}{3}-\dfrac{1}{39}\)
\(2C=\dfrac{4}{13}\)
\(C=\dfrac{2}{13}\)
\(C=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{37.39}\)
\(C=\frac{1}{2}.\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{37.39}\right)\)
\(C=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{37}-\frac{1}{39}\right)\)
\(C=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{39}\right)\)
\(C=\frac{1}{2}.\frac{12}{39}\)
\(C=\frac{4}{26}=\frac{2}{13}\)
Đặt \(A=\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}\)
\(\Leftrightarrow A=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+\frac{1}{11.13}\)
\(\Leftrightarrow2A=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+\frac{2}{11.13}\)
\(\Leftrightarrow2A=\frac{5-3}{3.5}+\frac{7-5}{5.7}+\frac{9-7}{7.9}+\frac{11-9}{9.11}+\frac{13-11}{11.13}\)
\(\Leftrightarrow2A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\)
\(\Leftrightarrow2A=\frac{1}{3}-\frac{1}{13}\)
\(\Leftrightarrow2A=\frac{13}{39}-\frac{3}{39}\)
\(\Leftrightarrow2A=\frac{10}{39}\)
\(\Leftrightarrow A=\frac{10}{39}\div2\)
\(\Leftrightarrow A=\frac{20}{39}\)
**** cho minn nhe
637.527-189 =637.526+637.1-189 =637.526+448 =1
526.637+448 637.526+448 637.526+448