Advertisements (Quảng cáo)
Tính:
\(a){{ – 1} \over {21}} + {{ – 1} \over {28}};\)
\(b){{ – 8} \over {18}} – {{15} \over {27}};\)
\(c){{ – 5} \over {12}} + 0,75;\)
\(d)3,5 – \left( { – {2 \over 7}} \right)\)
\(a){{ – 1} \over {21}} + {{ – 1} \over {28}} = {{ – 4} \over {84}} + {{ – 3} \over {84}} = {{ – 7} \over {84}} = {{ – 1} \over {12}}\)
Advertisements (Quảng cáo)
\(b){{ – 8} \over {18}} – {{15} \over {27}} = {{ – 8} \over {18}} + \left( { – {{15} \over {27}}} \right) = {{ – 4} \over 9} + {{ – 5} \over 9} = {{ – 9} \over 9} = – 1\)
\(c){{ – 5} \over {12}} + 0,75 = {{ – 5} \over {12}} + {3 \over 4} = {{ – 5 + 9} \over {12}} = {4 \over {12}} = {1 \over 3}\)
\(d)3,5 – \left( { – {2 \over 7}} \right) = 3,5 + {2 \over 7} = {{35} \over {10}} + {2 \over 7} = {7 \over 2} + {2 \over 7} = {{49 + 4} \over {14}} = {{53} \over {14}} = 3{{11} \over {14}}\)