a,2.(x-1)-86=14 b, 9.x-13=671 c, 31.(x-405).67=0 d, 3.(x+7)-21=51 e, 4.(x+5)+44=100

Đáp án:

\(\eqalign{
& a)\,x = 51 \cr
& b)\,\,x = 76 \cr
& c)\,\,x = 405 \cr
& d)\,\,x = 17 \cr
& e)\,\,x = 9 \cr} \)

Giải thích các bước giải:

\(\eqalign{
& a)\,\,2\left( {x – 1} \right) – 86 = 14 \cr
& \Leftrightarrow 2\left( {x – 1} \right) = 14 + 86 \cr
& \Leftrightarrow 2\left( {x – 1} \right) = 100 \cr
& \Leftrightarrow x – 1 = 50 \cr
& \Leftrightarrow x = 51 \cr
& b)\,\,9x – 13 = 671 \cr
& \Leftrightarrow 9x = 671 + 13 \cr
& \Leftrightarrow 9x = 684 \cr
& \Leftrightarrow x = 76 \cr
& c)\,\,31\left( {x – 405} \right).67 = 0 \cr
& \Leftrightarrow x – 405 = 0 \cr
& \Leftrightarrow x = 405 \cr
& d)\,\,3\left( {x + 7} \right) – 21 = 51 \cr
& \Leftrightarrow 3\left( {x + 7} \right) = 51 + 21 \cr
& \Leftrightarrow 3\left( {x + 7} \right) = 72 \cr
& \Leftrightarrow x + 7 = 24 \cr
& \Leftrightarrow x = 17 \cr
& e)\,\,4\left( {x + 5} \right) + 44 = 100 \cr
& \Leftrightarrow 4\left( {x + 5} \right) = 100 – 44 \cr
& \Leftrightarrow 4\left( {x + 5} \right) = 56 \cr
& \Leftrightarrow x + 5 = 14 \cr
& \Leftrightarrow x = 9 \cr} \)