Bài 3:
Có thể chia được nhiều nhất 20 phần quà vì UCLN(400;200;140)=20
Khi đó, mỗi phần có 20 quyển vở, 10 bút bi và 7 bút chì
Bài 2:
a: =>100+x=21
hay x=-79
b: \(\Leftrightarrow3^x\cdot3+3^x\cdot9+4=7\cdot16\)
\(\Leftrightarrow3^x=81\)
hay x=4
bài 2 :
\(a)113-\left(13-x\right)=21\\ \Leftrightarrow113-13+x=21\\ \Leftrightarrow100+x=21\\ \Leftrightarrow x=-79\\ b)3^{x+1}+\left(3^{x+2}+4\right)=7\cdot2^4\\ \Leftrightarrow3\cdot3^x+9\cdot3^x=108\\ \Leftrightarrow\left(3+9\right)\cdot3^x=108\\ \Leftrightarrow12\cdot3^x=108\\ \Leftrightarrow3^x=9\\ \Leftrightarrow3^x=3^2\\ \Leftrightarrow x=2\\ c)\Rightarrow\left(x+4+x+5\right)⋮9\\ \Leftrightarrow\left(2x+9\right)⋮9\\ \Rightarrow2x⋮9\\ \Rightarrow x=0\left(L\right);x=9\\ d)\Rightarrow\dfrac{3x+4}{x-1}\in Z\\ \Leftrightarrow\dfrac{3x-3+7}{x-1}\in Z\\ \Leftrightarrow\dfrac{3\left(x-1\right)+7}{x-1}\in Z\\ \Leftrightarrow3+\dfrac{7}{x-1}\in Z\\ \Rightarrow\dfrac{7}{x-1}\in Z\\ x\in Z,\dfrac{7}{x-1}\in Z\Rightarrow7⋮\left(x-1\right)\\ \Leftrightarrow\left(x-1\right)\in\text{Ư}\left(7\right)\\ \Leftrightarrow\left(x-1\right)\in\left\{\pm1;\pm7\right\}\\ \Leftrightarrow x\in\left\{-6;0;2;8\right\}\)
Bai 1 :
\(A=53\cdot47+53^2-2021^0\\ A=53\cdot47+53\cdot53-1\\ A=53\left(47+53\right)-1\\ A=53\cdot100-1\\ A=5300-1=5299\\ \Rightarrow B=38-21-58-69\\ B=\left(38-58\right)-\left(21+69\right)=\left(-20\right)-90\\ B=-110\\ \Rightarrow C=2020+27-2020+73-129\\ C=\left(2020-2020\right)+\left(27+73\right)-129\\ C=0+100-129\\ C=-29\)
bài 1:
\(D=\left(1-3\right)+\left(5-7\right)+\left(9-11\right)+...+\left(2017-2019\right)+2021\\ D=\left(-2\right)+\left(-2\right)+9-2+...\left(-2\right)2021\\ D=\left(-2\right)\cdot505+2021\\ D=\left(-1010\right)+2021\\ D=1010\)
