x=5 

tick tớ nhé 

(1+y)/9=1+2y/7

=>(1+y).7=(1+2y).9

=>7+7y=9+18y

=>y=-2/11

=>(1+-2/11)/9=(1+3.(-2/11)/x

=>1/11=5/11.x

=>x=5

đã túng rồi lại găp lũ ngu

x = 5

tick nhé !

Ta có:

\(\frac{1+2y}{7}=\frac{1+y}{9}\Rightarrow\frac{2.\left(1+2y\right)}{2.7}=\frac{1+y}{9}\)

\(\Rightarrow\frac{2+4y}{14}=\frac{1+y}{9}\)

Áp dụng tính chất dãy tỉ óố bằng nhau, ta có:

\(\frac{2+4y}{14}=\frac{1+y}{9}=\frac{2+4y-\left(1+y\right)}{14-9}=\frac{1+3y}{5}=\frac{1+3y}{x}\)

\(\Rightarrow x=5\)

Thay \(x=-1;y=-\dfrac{1}{2}\) vào \(A=-5x^3y-14xy^2-9-12x^2y\)

\(\Rightarrow A=-5.\left(-1\right)^3.\left(-\dfrac{1}{2}\right)-14.\left(-1\right).\left(-\dfrac{1}{2}\right)^2-9-12.\left(-1\right)^2.\left(-\dfrac{1}{2}\right)\)

\(\Rightarrow A=-\dfrac{5}{2}+\dfrac{7}{2}-9+6\)

\(\Rightarrow A=-2\)

\(A=-5x^3y-14xy^2-9-12x^2y\)

Thay \(x=-1;y=-\dfrac{1}{2}\) vào A

\(A=-5.\left(-1\right)^3.\left(-\dfrac{1}{2}\right)-14.\left(-1\right).\left(-\dfrac{1}{2}\right)^2-9-12.\left(-1\right)^2.\left(-\dfrac{1}{2}\right)=-2\)

Vậy với \(x=-1;y=-\dfrac{1}{2}\) thì A \(=-2\)

1+y/9=1+2y/7=>9(1+2y)=7(1+y)=>9+18y=7+7y=>18y-7y=7-9=>11y=-2=>y=-2/11.

=>1+2y/7=1+2(-2/11)/7=11

=>1+3y/x=11=>1+3(-2/11)/x=11=>(5/11)/x=11=>x=5

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