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a: UM=AU=2,5/2=1,25cm
VA=VE=AE/2=1,25cm
b: UV=1,25+1,25=2,5cm
Để A nguyên thì -11 chia hết cho n
=>\(n\in\left\{1;-1;11;-11\right\}\)
2n + 1 ⋮ n + 7
<=> 2(n + 7) - 13 ⋮ n + 7
<=> 13 ⋮ n + 7 (vì 2(n + 7) ⋮ n + 7)
<=> n + 7 ∈ Ư(13) = {1; -1; 13; -13}
n + 7 = 1 => n = -6
n + 7 = -1 => n = -8
n + 7 = 13 => n = 6
n + 7 = -13 => n = -20
Vậy n ∈ {-6; -8; 6; -20}
Ta có n-3\(⋮n+2\)
=> (n+2)-5\(⋮\)n+2
=> 5\(⋮\)n+2 vì n+2\(⋮\)n+2
Vì n\(\in\)Z=>n+2\(\in Z\)
\(\Rightarrow\)n+2\(\in\)Ư(5)={-1;-5;1;5}
Cậu lập bảng ra làm tiếp nhé!
\(n-3⋮n+2\)
ta có \(n+2⋮n+2\)
mà \(n-3⋮n+2\)
\(\Rightarrow n+2-\left(n-3\right)⋮n+2\)
\(\Rightarrow n+2-n+3⋮n+2\)
\(\Rightarrow5⋮n+2\)
\(\Rightarrow n+2\in\text{Ư}_{\left(5\right)}\)
\(\text{Ư}_{\left(5\right)}=\text{ }\left\{1;-1;5;-5\right\}\)
lập bảng giá trị
\(n+2\) | \(1\) | \(-1\) | \(5\) | \(-5\) |
\(n\) | \(-1\) | \(-3\) | \(3\) | \(-7\) |
vậy................
\(1,\dfrac{8}{13}+\dfrac{5}{13}=\dfrac{8+5}{13}=\dfrac{13}{13}=1\)
\(2,\dfrac{-8}{7}+\dfrac{-6}{7}=\dfrac{\left(-8\right)+\left(-6\right)}{7}=\dfrac{-14}{7}=-2\)
\(5,\dfrac{7}{-9}-\dfrac{13}{9}=\dfrac{\left(-7\right)-13}{9}=\dfrac{-20}{9}\)
\(6,\dfrac{5}{7}-\dfrac{-3}{21}=\dfrac{15}{21}-\dfrac{-3}{21}=\dfrac{15-\left(-3\right)}{21}=\dfrac{18}{21}=\dfrac{6}{7}\)
\(9,\dfrac{7}{-10}-\dfrac{2}{-15}=\dfrac{-105}{150}-\dfrac{-20}{150}=\dfrac{-\left(105-20\right)}{150}=\dfrac{-85}{150}\)
\(10,\dfrac{6}{13}-\dfrac{-15}{39}=\dfrac{18}{39}-\dfrac{-15}{39}=\dfrac{18-\left(-15\right)}{39}=\dfrac{33}{39}=\dfrac{11}{13}\)
1) \(\dfrac{8}{13}+\dfrac{5}{13}=\dfrac{13}{13}=1\)
2 ) \(\dfrac{-8}{7}+\dfrac{-6}{7}=\dfrac{-14}{7}=-2\)
3 ) \(\dfrac{-4}{3}-\dfrac{-7}{3}\)\(=\dfrac{3}{3}=1\)
4 ) \(\dfrac{-8}{5}+\dfrac{6}{-5}=\dfrac{-8}{5}+\dfrac{-6}{5}\)\(=\dfrac{-14}{5}\)
5 ) \(\dfrac{7}{-9}-\dfrac{13}{9}=\dfrac{-7}{9}-\dfrac{13}{9}=\dfrac{-20}{9}\)
6 ) \(\dfrac{5}{7}-\dfrac{-3}{21}=\dfrac{5\times3}{7\times3}=\dfrac{15}{21}-\dfrac{-3}{21}=\dfrac{18}{21}\)\(=\dfrac{6}{7}\)
Đợi
Bài 8:
a: -5/17<0<2/7
b: -11/10<-1<-9/14
c: 7/6>1>99/100
d: 7/15=35/75
8/25=24/75
11/75=11/75
mà 11<24<35
nên 11/75<8/25<7/15