Question

Answer 1

1:

a: 

a/b=3/4

=>a/3=b/4=k

=>a=3k; b=4k

\(A=\dfrac{2a-5b}{a-3b}=\dfrac{6k-20k}{3k-12k}=\dfrac{-14}{-9}=\dfrac{14}{9}\)

b: \(B=xy\left(xy+1\right)=1\cdot\dfrac{3}{2}\cdot\left(1\cdot\dfrac{3}{2}+1\right)=\dfrac{3}{2}\cdot\dfrac{5}{2}=\dfrac{15}{4}\)

2:

\(A=\dfrac{3b-b+1}{2b+1}=\dfrac{2b+1}{2b+1}=1\)

\(B=\left(2^2+\left(-3\right)^2\right)\left(2-3\right)^2=4+9=13\)

3: \(A=\dfrac{3\left(b-7\right)-2b}{2\left(b-7\right)+7b}=\dfrac{3b-21-2b}{2b-14+7b}=\dfrac{b-21}{9b-14}\)

b: 2x=3y

mà x+y=10

nên x=6; y=4

\(B=\left(6-3\right)\left(4-3\right)=3\)