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7/13 x 7/15 - 5/12 x 7/13 + 7/13 x 8/15 =7/13x(7/15-5/12+8/15)=7/13x7/12=49/156
12/13×8/15×7/9=........................
........................
`@` `\text {Ans}`
`\downarrow`
`x^3 = 125`
`=> x^3 = 5^3`
`=> x = 5`
Vậy, `x = 5`
_____
`4^5 \div 4^3`
`=`\(4^{5-3}\)
`= 4^2`
______
\(8^{12}\cdot8^3\div8^{15}\)
`=`\(8^{12+3-15}\)
`=`\(8^0=1\)
______
\(7^{15}\div7^{13}\)
`=`\(7^{15-13}\)
`=`\(7^2\)
_______
\(17^{15}\cdot17^{10}\div17^{22}\)
`=`\(17^{15+10-22}\)
`= 17^3`
_______
\(5^{10}\cdot25\div5^{11}\)
`=`\(5^{10}\cdot5^2\div5^{11}\)
`=`\(5^{10+2-11}\)
`= 5`
_______
\(15^{10}\cdot225\div15^{11}\)
`=`\(15^{10}\cdot15^2\div15^{11}\)
`=`\(15^{12}\div15^{11}\)
`= 15`
`@` `\text {Kaizuu lv uuu}`
\(x^3=125\)
\(\Rightarrow x^3=5^3\)
\(\Rightarrow x=3\)
___________________
\(4^5:4^3\)
\(=4^{5-3}\)
\(=4^2=16\)
___________________
\(8^{12}.8^3:8^{15}\)
\(=8^{15}:8^{15}\)
\(=1\)
___________________
\(7^{15}:7^{13}\)
\(=7^{15-13}\)
\(=7^2=49\)
___________________
\(17^{15}.17^{10}:17^{22}\)
\(=17^{25}:17^{22}\)
\(=17^3=4913\)
___________________
\(5^{10}.25:5^{11}\)
\(=5^{10}.5^2:5^{11}\)
\(=5^{12}:5^{11}\)
\(=5^1=5\)
___________________
\(15^{10}.225:15^{11}\)
\(=15^{10}.15^2:15^{11}\)
\(=15^{12}:15^{11}\)
\(=15^1=15\)
__________________
* an . am = an+m
an : am = an-m
Chúc bạn học tốt
Câu 30:
\(\dfrac{x+1}{8}=\dfrac{2}{x+1}\)
=>\(\left(x+1\right)^2=2\cdot8=16\)
=>\(\left[{}\begin{matrix}x+1=4\\x+1=-4\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=3\\x=-5\end{matrix}\right.\)
=>Chọn D
Câu 31:
\(-\dfrac{7}{15}\cdot\dfrac{5}{8}\cdot\dfrac{15}{-7}\cdot\left(-16\right)\)
\(=\dfrac{5}{8}\cdot\left(-16\right)=-10\)
=>Chọn D
15 × (4 - 7) - 15 × (5 - 3)
= 15 × (-3) - 15 × 2
= 15 × (-3 - 2)
= -15 × 5
= -75
--------
73 × (8 - 59) - 59 × (8 - 73)
= 73 × 8 - 73 × 59 - 59 × 8 + 59 × 73
= 8 × (73 - 59) + 73 × (59 - 59)
= 8 × 14 + 73 × 0
= 8 × 14
= 112
15 x (4-7) - 15 x (5-3)
= 15 x (-3) - 15 x (-2)
= 15 x (-3 - (-2))
= 15 x (-1)
= -15
73 x (8-59) - 59 x (8-73)
= 73 x 8 - 59 x 73 - 59 x (-65)
= 73 x 8 - 59 x (73 - (-65))
= 73 x 8 - 59 x 8
= 8 x (73-59)
= 8 x 14
= 112
a) 84
b) -300
c) 1700
a) = 10 . ( 7.8 )
= 10 . 56
= 560
b)
= 9.2.7.5
= ( 9.7 ) . ( 2.5 )
= 63 . 10
= 630
b) 7.x=42
x = 42 : 7
x = 6
c) 180 : x = -12
x = 180 : ( -12 )
x = -15
6) 8(x – |-7|) – 6(x – 2) = |-8|.6 – 50
7) -7(5 – x) – 2(x – 10) = 15
8) 4(x – 1) – 3(x – 2) = -|-5|
a) Ta có: \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)
nên -11<x<-8
hay \(x\in\left\{-10;-9\right\}\)
b) Ta có: \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)
\(\Leftrightarrow\dfrac{9}{21}< \dfrac{x}{21}< \dfrac{14}{21}\)
Suy ra: 9<x<14
hay \(x\in\left\{10;11;12;13\right\}\)
c) Ta có: \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)
nên \(\dfrac{-536}{168}< \dfrac{x}{168}< \dfrac{-63}{168}\)
Suy ra: -536<x<-63
hay \(x\in\left\{-535;-534;...;-64\right\}\)
15 + x = 15
x = 15 -15
x = 0
15+x=7-(-8)
15+x=7+8
15+x=15
x=15-15
x=0
vậy x=0