Bài 114: trang 32 sbt Toán 6 tập 2
Tìm x biết
a) \(0,5x - {2 \over 3}x = {7 \over {12}}\) | b) \(x \div 4{1 \over 3} = - 2,5\) |
c) \(5,5x = {{13} \over {15}}\) | d) \(\left( {{{3x} \over 7} + 1} \right):\left( { - 4} \right) = {{ - 1} \over {28}}\) |
Bài Làm:
a) \(0,5x - {2 \over 3}x = {7 \over {12}} \)
\(x.\left( {{1 \over 2} - {2 \over 3}} \right) = {7 \over {12}} \)
\(x.\left( {{3 \over 6} - {4 \over 6}} \right) = {7 \over {12}} \)
\(x.{{ - 1} \over 6} = {7 \over {12}} \)
\(x = {7 \over {12}} \div {{ - 1} \over 6}\)
\(x={7 \over {12}} . (-6)\)
\(x=-\frac{7}{2}=-3,5\)
b) \(x \div 4{1 \over 3} = - 2,5 \)
\(x \div {{13} \over 3} = {{ - 5} \over 2} \)
\(x = {{ - 5} \over 2}.{{13} \over 3} \)
\(x = {{ - 65} \over 6} \)
\(x= - 10{5 \over 6} \)
c) \(5,5x = {{13} \over {15}} \)
\({{55} \over {10}}x = {{13} \over {15}} \)
\(x = {{13} \over {15}} \div {{55} \over {10}} \)
\(x = {{13} \over {15}}.{{10} \over {55}} \)
\(x = {{26} \over {165}}\)
d) \(\left( {{{3x} \over 7} + 1} \right) \div \left( { - 4} \right) = {{ - 1} \over {28}} \)
\({{3x} \over 7} + 1 = {{ - 1} \over {28}}.\left( { - 4} \right) \)
\({{3x} \over 7} = {1 \over 7} - 1 \)
\({{3x} \over 7} = {{ - 6} \over 7} \)
\(3x= - 6 \)
\(x = - 6 \div 3 = - 2\)