Advertisements (Quảng cáo)
Tính bằng cách hợp lý:
\({\rm{A}} = ( – 5,85) + \left\{ {\left[ {\left( { + 41,3} \right) + \left( { + 5} \right)} \right] + \left( { + 0,85} \right)} \right\}\)
\(B = \left( { – 87,5} \right) + \left\{ {\left( { + 87,5} \right) + \left[ {\left( { + 3,8} \right) + ( – 0,8)} \right]} \right\}\)
\(C = \left[ {\left( { + 9,5} \right) + \left( { – 13} \right)} \right] + \left[ {\left( { – 5} \right) + \left( { + 8,5} \right)} \right]\)
Advertisements (Quảng cáo)
\(\eqalign{
& {\rm{A}} = ( – 5,85) + \left\{ {\left[ {\left( { + 41,3} \right) + \left( { + 5} \right)} \right] + \left( { + 0,85} \right)} \right\} \cr
& = \left\{ {\left( { – 5,85} \right) + \left[ {\left( { + 5} \right) + \left( { + 0,85} \right)} \right]} \right\} + \left( { + 41,3} \right) \cr
& = \left\{ {\left( { – 5,85} \right) + \left( { + 5,85} \right)} \right\} + \left( { + 41,3} \right) \cr
& = 41,3 \cr} \)
\(\eqalign{
& B = \left( { – 87,5} \right) + \left\{ {\left( { + 87,5} \right) + \left[ {\left( { + 3,8} \right) + ( – 0,8)} \right]} \right\} \cr
& = \left[ {\left( { – 87,5} \right) + \left( { + 87,5} \right)} \right] + \left[ {\left( { – 3,8} \right) + ( – 0,8)} \right] \cr
& = 0 + 3 = 3 \cr} \)
\(\eqalign{
& C = \left[ {\left( { + 9,5} \right) + \left( { – 13} \right)} \right] + \left[ {\left( { – 5} \right) + \left( { + 8,5} \right)} \right] \cr
& = \left[ {\left( { + 9,5} \right) + \left( { + 8,5} \right)} \right] + \left[ {\left( { – 13} \right) + ( – 5)} \right] \cr
& = 18 + ( – 18) = 0 \cr} \)
Mục lục môn Toán 7 (SBT)