Bài 95 trang 45 sgk Toán 7 – tập 1, Tính giá trị biểu thức:...

Bài 95. Tính giá trị biểu thức: 

(A =  – 5,13:left( {5{5 over {28}} – 1{8 over 9}.1,25 + 1{{16} over {63}}} ight))

(B = left( {3{1 over 3}.1,9 + 19,5:4{1 over 3}} ight).left( {{{62} over {75}} – {4 over {25}}} ight))

Giải

(eqalign{
& A = – 5,13:left( {5{5 over {28}} – 1{8 over 9}.1,25 + 1{{16} over {63}}} ight) cr
& = – 5,13:left( {{{145} over {28}} – {{17} over 9}.{{125} over {100}} + {{79} over {63}}} ight) cr
& = – 5,13:left( {{{145} over {28}} – {{17} over 9}.{5 over 4} + {{79} over {63}}} ight) cr
& = – 5,13:left( {{{145} over {28}} – {{85} over {36}} + {{79} over {63}}} ight) cr
& = – 5,13:{{57} over {14}} = – 5,13.{{14} over {57}} cr
& = {{ – 71,82} over {57}} = -1,26 cr} )

(eqalign{
& B = left( {3{1 over 3}.1,9 + 19,5:4{1 over 3}} ight).left( {{{62} over {75}} – {4 over {25}}} ight) cr
& = left( {{{10} over 3}.1,9 + 19,5:{{13} over 3}} ight).left( {{{62 – 12} over {75}}} ight) cr
& = left( {{{19} over 3} + {{58,5} over {13}}} ight).{{50} over {75}} cr
& = left( {{{19} over 3} + 4,5} ight).{2 over 3} cr
& = {{19 + 13,5} over 3}.{2 over 3} cr
& = {{32,5} over 3}.{2 over 3} = {{65} over 9} = 7{2 over 9} cr} )