Question

1.viết tất cả các tỉ lệ thức từ các đẳng thức sau

a) 3*5=-1*-15

b) 4*9=-3*-12

c)3*b=7*c

d) a*x=b*y

2.tìm x

a) \(\dfrac{x-1}{4}=\dfrac{9}{x-1}\)

b)\(\dfrac{x+2}{5}=\dfrac{20}{x+2}\)

Answer 1

2.

a) \(\dfrac{x-1}{4}=\dfrac{9}{x-1}\)

\(\Leftrightarrow\left(x-1\right)^2=9.4\)

\(\Leftrightarrow\left(x-1\right)^2=36\)

\(\Leftrightarrow\left(x-1\right)^2=\left[{}\begin{matrix}6^2\\-6^2\end{matrix}\right.\)

\(\Leftrightarrow x-1=\left[{}\begin{matrix}6\\-6\end{matrix}\right.\)

\(\Leftrightarrow x=\left[{}\begin{matrix}7\\-5\end{matrix}\right.\)

Answer 2

1. a. \(\dfrac{3}{-1}=\dfrac{-15}{5}\); \(\dfrac{-1}{3}=\dfrac{5}{-15}\)

\(\dfrac{3}{-15}\)= \(\dfrac{5}{-1}\); \(\dfrac{-15}{3}=\dfrac{-1}{5}\)

b. \(\dfrac{4}{-3}=\dfrac{-12}{9};\dfrac{-3}{4}=\dfrac{9}{-12}\)

\(\dfrac{4}{-12}=\dfrac{9}{-3};\dfrac{-12}{4}=\dfrac{-3}{9}\)

c. \(\dfrac{3}{7}=\dfrac{c}{b};\dfrac{7}{3}=\dfrac{b}{c}\)

\(\dfrac{3}{c}=\dfrac{b}{7};\dfrac{c}{3}=\dfrac{7}{b}\)

d. \(\dfrac{a}{b}=\dfrac{y}{x};\dfrac{b}{a}=\dfrac{x}{y}\)

\(\dfrac{a}{y}=\dfrac{x}{b};\dfrac{y}{a}=\dfrac{b}{x}\)

chúc bạn học tốt

Answer 3

Câu 2: 

a: =>(x-1)²=36

=>x-1=6 hoặc x-1=-6

=>x=7 hoặc x=-5

b: =>(x+2)²=100

=>x+2=10 hoặc x+2=-10

=>x=8 hoặc x=-12