Bai 1 :
a/ \(x:1,4+2,8=8,4\)
\(x:1,4=8,4-2,8\)
\(x:1,4=5,6\)
\(x=5,6\times1,4\)
\(x=7,84\)
b/ \(2,8:x-1,5=2,3:5,75\)
\(2,8:x-1,5=\frac{2}{5}\)
\(2,8:x=\frac{2}{5}+1,5\)
\(2,8:x=\frac{19}{10}=1,9\)
\(\Rightarrow x=2,8:1,9=\frac{28}{19}\)
Bai 2 :
a/ \(575-\left(6\times x+70\right)=445\)
\(6\times x+70=575-445\)
\(6\times x+70=130\)
\(6\times x=130-70\)
\(\Rightarrow6\times x=60\Rightarrow x=10\)
b/ \(315+\left(125-x\right)=435\)
\(125-x=435-315\)
\(125-x=120\)
\(\Rightarrow x=5\)
c/ \(\left(x-105\right):21=15\)
\(x-105=15\times21\)
\(x-105=315\)
\(\Rightarrow x=420\)
d/ \(3636:\left(12\times x-91\right)=36\)
\(12\times x-91=3636:36\)
\(12\times x-91=101\)
\(12\times x=101+91\)
\(12\times x=192\)
\(\Rightarrow x=16\)
e/ \(12\times\left(x-5\right)+73=20\)
\(12\times\left(x-5\right)=20-73\)
\(12\times\left(x-5\right)=-53\)
\(x-5=-53:12\)
\(x-5=\frac{-53}{12}\)
\(\Rightarrow x=\frac{-53}{12}+5\)
\(\Rightarrow x=\frac{7}{12}\)
f/ \(\left[\left(10-x\right)\times2+5\right]:3-2=3\)
\(\left[\left(10-x\right)\times2+5\right]:3=3+2\)
\(\left[\left(10-x\right)\times2+5\right]:3=5\)
\(\left[\left(10-x\right)\times2+5\right]=5\times3\)
\(\left(10-x\right)\times2+5=15\)
\(\left(10-x\right)\times2=15-5\)
\(\left(10-x\right)\times2=10\)
\(10-x=10:2\)
\(10-x=5\)
\(\Rightarrow x=5\)
dễ mà bạn.......bạn chỉ cần thực hiện theo đúng thứ tự của phép tính ; nhân chia trước, cộng trừ sau và nắm rõ quy tắc đoi dau
1.
a) x : 1,4 = 8,4-2,8=5,6
x= 5,6 x 1,4=7,84
b)2,8 :x -1,5 = 0,4
2,8 : x = 1,9
x= 2,8:1,9=1,47
2
a, 575 - ( 6 × x + 70 ) = 445
6x+70=130
6x=60
x=10
b,315 + ( 125 - x ) = 435
125-x=435-315=120
x=125-120=5
c, ( x - 105 ) : 21 = 15
(x-105)=15 . 21 = 315
x=315+105=420
d, 3636 : ( 12 × X - 91 ) = 36
12x-91=3636:36=101
12x=101 + 91 = 192
x= 192 : 12=16
e, 12 × ( X - 5 ) + 73 = 20
12(x-5) = -53
x-5=-53/12
x=7/12
f, [ (10 - x ) × 2 + 5 ] : 3 - 2 = 3
[(10-x)2+5]:3 = 3+2 =5
(10-x)2 +5 = 5.3=15
(10-x)2 = 10
10-x=5
x=10-5=5
a) \(x\div1,4+2,8=8,4\)
\(\Leftrightarrow x\div1,4=8,4-2,8\)
\(\Leftrightarrow x\div1,4=5,6\)
\(\Leftrightarrow x=5,6\times1,4\)
\(\Leftrightarrow x=7,84\)
