Tìm x
24 − x = 7
59 − x = 16
60 − x = 38
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a) – 1 < x < 49 18 => x ∈ {0;1;2}
b) − 1 24 < x 24 < 1 14 => x = 0
c) 2 3 ≤ x ≤ 26 5 => x ∈ {1;2;3;4;5}
d) 0 < x ≤ 1 => x = 1
`@` `\text {Ans}`
`\downarrow`
`23 + 23 \times 45 + 23 \times 44`
`= 23 \times (1+45 + 44)`
`= 23 \times 90`
`= 2070`
`b)`
`36 \times 280 - 9 \times 79 \times 4 - 36`
`= 36 \times 280 - 9 \times 4 \times 79 - 36`
`= 36 \times 280 - 36 \times 79 - 36`
`= 36 \times (280 - 79 - 1)`
`= 36 \times 200`
`= 7200`
`c)`
`8 \times 9 \times 10 + 6 \times 25 \times 12 + 4 \times 18 \times 66 - 2 \times 36`
`= 2 \times 4 \times 9 \times 10 + 6 \times 2 \times 6 \times 25 + 2 \times 2 \times 18 \times 66 - 2 \times 36`
`= 10 \times 2 \times 36 + 36 \times 2 \times 25 + 36 \times 2 \times 66 - 2 \times 36`
`= 36 \times 2 \times (10 + 25 + 66 - 1)`
`= 72 \times 100`
`= 7200`
_____
`c)`
`439 \times 78 - 38 \times 78 - 78`
`= 78 \times (439 - 38 - 1)`
`= 78 \times 400`
`= 31200`
`d)`
`24 \times 13 + 6 \times 89 \times 4 - 2 \times 24`
`= 24 \times 13 + 24 \times 89 - 2 \times 24`
`= 24 \times (13 + 89 - 2)`
`= 24 \times 100`
`= 2400`
$2,21:x=85$
$x=2,21:85$
$x=0,026$
$---$
$24\times x=101,3-12,5$
$24\times x=88,8$
$x=88,8:24$
$x=3,7$
$---$
$(x+2,9)\times24=292,32$
$x+2,9=292,32:24$
$x+2,9=12,18$
$x=12,18-2,9$
$x=9,28$
2,21:x=85 x=2,21;85 x=0,026 24xX=101,3-12,5 24xX=88,8 X=88,8;24 X=3,7 (X+2,9)x24=292,32 (X+2,9) =292,32:24 (X+2,9) =12,18 X =12,18-2,9 X =9,28 Nhớ tick cho mình nha!
Đáp án cần chọn là: B
x∈{−1;0;1;2;3;4;5}
5 6 + − 7 8 ≤ x 24 ≤ − 5 12 + 5 8 − 1 24 ≤ x 24 ≤ 5 24 − 1 ≤ x ≤ 5
- 7 8 + 5 6 < x 24 ≤ 5 8 + - 5 12
⇔ - 21 24 + 20 24 ≤ x 24 ≤ 15 24 + - 10 24 ⇔ - 1 24 ≤ x 24 ≤ 5 24
-1 ≤ x ≤ 5 mà x ∈ Z. Do đó: x ∈ { -1 ; 0 ; 1 ; 2 ; 3 ; 4 ; 5 }
\(A=\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+...+\dfrac{1}{120}\)
\(=2\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+...+\dfrac{1}{240}\right)\)
\(=2\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{15.16}\right)\)
\(=2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{15}-\dfrac{1}{16}\right)\)
\(=2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\)
\(=2\cdot\dfrac{3}{16}\)
\(=\dfrac{3}{8}\)
\(A:x=759\)
\(\dfrac{3}{8}:x=759\)
\(\Rightarrow x=\dfrac{3}{8}:759=\dfrac{1}{2024}\)
#AvoidMe
A=2(1/20+1/30+...+1/240)
=2(1/4-1/5+1/5-1/6+...+1/15-1/16)
=2*3/16=3/8
A:x=759
=>x=3/8:759=1/2024
-1 ≤ x ≤ 5 mà x ∈ Z. Do đó: x ∈ { -1 ; 0 ; 1 ; 2 ; 3 ; 4 ; 5 }
3^2x+3^X+3=759
(3x)^2+3^x=759-3=756
3^x.3^x+3^x=756
3^x(3^x+1)=756
3^x(3^x+1)=27x28
Vậy 3^x =27 và x = 3
24 − x = 7
X = 24 − 7
X = 17
59 − x = 16
X = 59 − 16
X = 43
60 − x = 38
X = 60 − 38
X = 22