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theo mình nghĩ là
( 112 x 115 ) x ( 113 x 114 ) x 116
sai thì cho xin lỗi nha bn
\(\frac{1}{2}\times\frac{1}{3}+\frac{1}{3}\times\frac{1}{4}+\frac{1}{4}\times\frac{1}{5}+\frac{1}{5}\times\frac{1}{6}\)
\(=\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(=\frac{1}{2}-\frac{1}{6}=\frac{2}{6}=\frac{1}{3}\)
\(\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{5}+\frac{1}{5}.\frac{1}{6}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(=\frac{1}{2}-\frac{1}{6}\)
\(=\frac{1}{3}\)
1) 1/5 . 5/4 + 1/5 . 5/4
= (1/5 + 1/5) . 5/4
= 1/5 . 5/4
= 1/4
2)tự làm
1.\(\frac{1}{5}\times\frac{5}{4}+\frac{1}{5}\times\frac{5}{4}\)
\(=\frac{1}{5}\times\frac{5}{4}\times2\)
\(=\frac{1\times5\times2}{5\times4}\)
\(=\frac{1}{2}\)
2.\(\frac{7}{6}\times\frac{2}{5}-\frac{1}{3}\times\frac{2}{5}+\frac{5}{6}\times\frac{2}{5}\)
\(=\frac{2}{5}\times\left(\frac{7}{6}-\frac{1}{3}+\frac{5}{6}\right)\)
\(=\frac{2}{5}\times\left(\frac{7}{6}-\frac{2}{6}+\frac{5}{6}\right)\)
\(=\frac{2}{5}\times\frac{5}{3}\)
\(=\frac{2}{3}\)
\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right).\left(1-\frac{1}{5}\right).\left(1-\frac{1}{6}\right)\)
\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.\frac{4}{5}.\frac{5}{6}\)
\(=\frac{1.2.3.4.5}{2.3.4.5.6}\)
\(=\frac{1}{6}\)
\(\left(1-\frac{1}{2}\right)\times\left(1-\frac{1}{3}\right)\times\left(1-\frac{1}{4}\right)\times\left(1-\frac{1}{5}\right)\times\left(1-\frac{1}{6}\right)\).
\(=\left(\frac{2}{2}-\frac{1}{2}\right)\times\left(\frac{3}{3}-\frac{1}{3}\right)\times\left(\frac{4}{4}-\frac{1}{4}\right)\times\left(\frac{5}{5}-\frac{1}{5}\right)\times\left(\frac{6}{6}-\frac{1}{6}\right)\).
\(=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}\times\frac{5}{6}\).
\(=\frac{1\times2\times3\times4\times5}{2\times3\times4\times5\times6}=\frac{1}{6}\).
=1/2*2/3*3/4*4/5*5/6
bn gạch các số có cùng tử số và mẫu số đi
=1/6
ai k mk thì mk k lại
=A*(4/2+1/2-5/2)
=A*(5/2-5/2)=0