\(Bài78\)
\(a.36\cdot68+68\cdot64=68\cdot\left(36+64\right)=68\cdot100=6800.\)
\(b.39\cdot113+87\cdot39=39\cdot\left(113+87\right)=39\cdot200=7800.\)
\(c.2^3\cdot15+2^3\cdot35=2^3\cdot\left(15+35\right)=8\cdot50=400.\)
\(d.\left[600-\left(40:2^3+3\cdot5^3\right)\right]:5=\left[600-\left(40:8+3\cdot125\right)\right]:5\)
\(=\left[600-380\right]:5=220:5=44.\)
\(Bài79\)
\(a.\left(x-35\right)-120=0\)
\(x-35-120=0\)
\(x-155=0\)
\(x=0+155\)
\(x=155.\)
\(Vậy...\)
\(b.310-\left(118-x\right)=217\)
\(-\left(118-x\right)=217-310\)
\(-\left(118-x\right)=-93\)
\(118-x=93\)
\(-x=93-119\)
\(-x=-25\)
\(x=25.\)
\(Vậy...\)
\(c.156-\left(x+61\right)=82\)
\(-\left(x+61\right)=82-156\)
\(-\left(x+61\right)=-74\)
\(x+61=74\)
\(x=74-61\)
\(x=13.\)
\(Vậy...\)
\(d.814\left(x-305\right)=712\)
\(x-305=712:814\)
\(x-305=\dfrac{356}{407}\)
\(x=\dfrac{346}{407}+305\)
\(x=\dfrac{124491}{407}.\)
\(Vậy...\)
\(e.2x-138=2^3\cdot3^2\)
\(2x-138=8\cdot9\)
\(2x-138=72\)
\(2x=72+138\)
\(2x=210\)
\(x=210:2\)
\(x=105.\)
\(Vậy...\)
\(g.5\left(x+35\right)=515\)
\(x+35=515:5\)
\(x+35=103\)
\(x=103-35\)
\(x=68.\)
\(Vậy...\)
\(h.20-\left[7\left(x-3\right)+4\right]-20=2\)
\(-\left[7\left(x-3\right)+4\right]=2-20\)
\(-\left[7\left(x-3\right)+4\right]=-18\)
\(-7x+17=-18\)
\(-7x=-18-17\)
\(-7x=-35\)
\(x=-35:\left(-7\right)\)
\(x=5.\)
\(Vậy...\)
\(i.\left[\left(6x-39\right):3\right]\cdot28=5628\)
\(56x-364=5628\)
\(56x=5628+364\)
\(56x=5992\)
\(x=5992:56\)
\(x=107.\)
\(Vậy...\)
Phần dưới tôi ko làm đâu nhé. Tại nó dài quá. bạn có thể tách các câu để hỏi từng cái nhé.
