Question

Cho   \(f\left(x\right)=\frac{x+2}{x-1}\)

a, Tính    \(f\left(7\right)\)

b, Tìm x để    \(f\left(x\right)=\frac{1}{4}\)

c, Tìm     \(x\in\)   Z

d, Tìm x để    \(f\left(x\right)>1\)

Answer 1

a) f (7) = \(\frac{7+2}{7-1}=\frac{9}{6}=\frac{3}{2}\)

b) ???

Answer 2

a)f(7)=9/6=3/2

b)x=-3

c)x=2

Answer 3

a, dễ quá r tự làm đi

b,\(f\left(x\right)=\frac{1}{4}<=>\frac{x+2}{x-1}=\frac{1}{4}<=>\frac{x-1+3}{x-1}<=>\frac{x-1}{x-1}+\frac{3}{x-1}=\frac{1}{4}\)

<=> \(1+\frac{3}{x-1}=\frac{1}{4}\)\(<=>\frac{3}{x-1}=\frac{1}{4}-1<=>\frac{3}{x-1}=\frac{3}{-4}<=>x-1=-4<=>x=-3\)

c,x ∈ Z \(<=>x+2\) \(\vdots\) \(x-1\)

\(<=>\)\(x-1+3\) \(\vdots\) \(x-1\)

\(=>3\) \(\vdots\)\(x-1\)

\(\Leftrightarrow x-1\text{∈}Ư\left(3\right)=\left\{1;-1;3;-3\right\}\)

x-1	1	-1	3	-3
x	2	0	4	-2