\(a,\) Khi \(x=4\) và \(y=9\), \(A=2\cdot4+9:3=8+3=11\)
\(b,\) Khi \(x=1\) và \(y=8\), \(B=\left(1+8\right)\cdot5-2\cdot1-8=9\cdot5-2-8=45-10=35\)
\(c,\) Khi \(x=6\) và \(y=5\), \(C=6\cdot\left(6+5\right)-5\cdot\left(5-4\right)=6\cdot11-5=66-5=61\)
a , Khi x = 4 và y = 9 , A = 2 ⋅ 4 + 9 : 3 = 8 + 3 = 11 b , Khi x = 1 và y = 8 , B = ( 1 + 8 ) ⋅ 5 − 2 ⋅ 1 − 8 = 9 ⋅ 5 − 2 − 8 = 45 − 10 = 35 c , Khi x = 6 và y = 5 , C = 6 ⋅ ( 6 + 5 ) − 5 ⋅ ( 5 − 4 ) = 6 ⋅ 11 − 5 = 66 − 5 = 61
\(a,2x-10=12\\ \Rightarrow x=\dfrac{22+10}{2}=11\)
\(b,18-3x=6\\ \Rightarrow x=\dfrac{6-18}{-3}=4\)
\(c,20:x+4=9\\ \Rightarrow20:x=5\\ \Rightarrow x=20:5=4\)
\(d,x:5-7=12\\ \Rightarrow x:5=19\\ \Rightarrow x=\dfrac{19}{5}\)
\(e,\left(28-x\right):4+12=17\\ \Rightarrow\left(28-x\right):4=5\\ \Rightarrow28-x=20\\ \Rightarrow x=8\)
\(f,2x+4x=30\\ \Rightarrow6x=30\Rightarrow x=5\)
\(g,x+4x=40\\ \Rightarrow5x=40\Rightarrow x=8\)
\(h,2\left(x+4\right)-18=30\\ \Rightarrow2\left(x+4\right)=48\\ \Rightarrow x+4=24\\ \Rightarrow x=20\)
\(i,2x-4\cdot8=12:3\\ \Rightarrow2x-32=4\\ \Rightarrow2x=36\\ \Rightarrow x=18\)
\(a,35+41+65=\left(35+65\right)+41=100+41=141\\ b,24+37+76+73=\left(24+76\right)+\left(37+73\right)=100+110=210\\ c,27\cdot45+27\cdot55=27\cdot\left(45+55\right)=27\cdot100=2700\\ d,2\cdot3\cdot5\cdot7=\left(2\cdot5\right)\cdot\left(3\cdot7\right)=10\cdot21=210\\ e,4\cdot11\cdot25\cdot9=\left(4\cdot25\right)\cdot\left(11\cdot9\right)=100\cdot99=9900\)
\(a,\) Khi \(x=10\) và \(y=3\), \(A=3\cdot10-5\cdot3+5=30-15+5=20\)
\(b,\) Khi \(x=5\) và \(y=6\), \(B=4\cdot\left(5+6\right)-2\cdot5-6=4\cdot11-10-6=44-10-6=28\)
Bài 2:
a. 2x - 10 = 12
⇔ 2x = 12 + 10
⇔ 2x = 22
⇔ x = 22/2 = 11
b. 18 - 3x = 6
⇔ 18 - 6 = 3x
⇔ 12 = 3x
⇔ x = 12/3 = 4
c. \(\dfrac{20}{x}+4=9\)
⇔ \(\dfrac{20}{x}+\dfrac{4x}{x}=\dfrac{9x}{x}\)
⇔ 20 + 4x = 9x
⇔ 20 = 9x - 4x
⇔ 20 = 5x
⇔ x = 20/5 = 4
d. \(\dfrac{x}{5}-7=12\)
⇔ \(\dfrac{x}{5}-\dfrac{35}{5}=\dfrac{60}{5}\)
⇔ x - 35 = 60
⇔ x = 60 + 35
⇔ x = 95
e. \(\dfrac{28-x}{4}+12=17\)
⇔ \(\dfrac{28-x}{4}+\dfrac{48}{4}=\dfrac{68}{4}\)
⇔ 28 - x + 48 = 68
⇔ 28 + 48 - 68 = x
⇔ x = 8
f. 2x + 4x = 30
⇔ 6x = 30
⇔ x = 30/6 = 5
g. x + 4x = 40
⇔ 5x = 40
⇔ x = 40/5 = 8
h. 2(x + 4) - 18 = 30
⇔ 2x + 8 - 18 = 30
⇔ 2x = 30 - 8 + 18
⇔ 2x = 40
⇔ x = 40/2 = 20
i. 2x - 4.8 = 12:3
⇔ 2x - 32 = 4
⇔ 2x = 4 + 32
⇔ 2x = 36
⇔ x = 36/2 = 18
Bài 3:
a. 35 + 41 + 65
= 35 + 65 + 41
= 100 + 41
= 141
b. 24 + 37 + 76 + 73
= (24 + 76) + (37 + 73)
= 100 + 110
= 210
c. 27.45 + 27.55
= 27(45 + 55)
= 27.100
= 2700
d. 2.3.5.7
= 2.5.3.7
= 10.21
= 210
e. 4.11.25.9
= 4.25.11.9
= 100.99
= 199
Bài 4:
a: Ta có: A=3x-5y+5
\(=3\cdot10-5\cdot3+5\)
\(=30-15+5=20\)
b: Ta có: \(B=4\left(x+y\right)-2x-y\)
\(=4x+4y-2x-y\)
=2x-3y
\(=2\cdot5-3\cdot6=-8\)
