II: Tự luận
Câu 4:
a) Để A là phân số thì \(2n-4\ne0\)
\(\Leftrightarrow2n\ne4\)
\(\Leftrightarrow n\ne2\)
b) Để A là số nguyên thì \(2n+2⋮2n-4\)
\(\Leftrightarrow2n-4+6⋮2n-4\)
mà \(2n-4⋮2n-4\)
nên \(6⋮2n-4\)
\(\Leftrightarrow2n-4\inƯ\left(6\right)\)
\(\Leftrightarrow2n-4\in\left\{1;-1;2;-2;3;-3;6;-6\right\}\)
\(\Leftrightarrow2n\in\left\{5;3;6;2;7;1;10;-2\right\}\)
hay \(n\in\left\{\dfrac{5}{2};\dfrac{3}{2};3;1;\dfrac{7}{2};\dfrac{1}{2};5;-1\right\}\)
I trắc nghiệm
1.d ; 2.b; 3.a; 4.d;5.c; 6.a;7.d; 8.d;9.c;10.a;11.c;12.b
II tự luận
câu 1
a, 3/5+-2/5=1/5
b, (4/5+1/2)(3/13-8/13)=13/10*(-5/13)=-1/2
c, -5/7*2/11+(-5/7)*9/11+1=-5/7(2/11+9/11)+1=-5/7*1+1=-5/7+7/7=2/7
câu 2
a, x-(-5/120=-7/12
x=-7/12+(-5/12)
x= -1
vậy ...
b, x/20=7/10+(-13/20)
x/20=1/20
x=1
vậy ...
câu 3 tự vẽ hình
ta có xOy+tOy=tOx
thay số: 35+toy=70
tOy=35
-Oy là tia pg của xOt
II. Tự luận
Câu 1:
a) \(\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)
b) \(\left(\dfrac{4}{5}+\dfrac{1}{2}\right).\left(\dfrac{3}{13}-\dfrac{8}{13}\right)\)
\(=\left(\dfrac{8}{10}+\dfrac{5}{10}\right).\dfrac{3-8}{13}\)
\(=\dfrac{13}{10}.\dfrac{-5}{13}\)
\(=\dfrac{-1}{2}\)
c) \(\dfrac{-5}{7}.\dfrac{2}{11}+\dfrac{-5}{7}.\dfrac{9}{11}+1\)
\(=\dfrac{-5}{7}.\left(\dfrac{2}{11}+\dfrac{9}{11}\right)+1\)
\(=\dfrac{-5}{7}.1+1\)
\(=\dfrac{2}{7}\)
Câu 2:
a) \(x-\dfrac{-5}{12}=\dfrac{-7}{12}\)
\(x=\dfrac{-7}{12}+\dfrac{-5}{12}\)
\(x=-1\)
Vậy \(x=-1\)
b) \(\dfrac{x}{20}=\dfrac{7}{10}+\dfrac{-13}{20}\)
\(\dfrac{x}{20}=\dfrac{14}{20}+\dfrac{-13}{20}\)
\(\dfrac{x}{20}=\dfrac{1}{20}\)
\(x=1\)
Vậy \(x=1\)
