Question

[Hùng Tô Hiến]

A=(3X+1)3-(y-2)2+(y-1)3+(x+y)2 tại x= -1/3 , y= -3

Answer 1

[Nguyễn Lê Phước Thịnh]

\(A=\left(3x+1\right)^3-\left(y-2\right)^2+\left(y-1\right)^3+\left(x+y\right)^2\)

Thay x=-1/3;y=3 vào A, ta được:

\(A=\left[3\cdot\dfrac{-1}{3}+1\right]^3-\left(3-2\right)^2+\left(3-1\right)^3+\left(-\dfrac{1}{3}+3\right)^2\)

\(=-1^2+2^3+\left(\dfrac{8}{3}\right)^2\)

\(=\dfrac{64}{9}+7=\dfrac{127}{9}\)

Answer 2

[Nguyễn Tuấn Tú]

\(A=\left(3x+1\right).3-\left(y-2\right).2+\left(y-1\right).3+\left(x+y\right).2\\ \Leftrightarrow A=3.\left(3x+1+y-1\right)+2.\left(x+y-y+2\right)\\ \Leftrightarrow A=3.\left(3x+y\right)+2.\left(x+2\right)\)
Thay \(x=-\dfrac{1}{3};y=-3\) được:
\(A=3.\left[3.\left(-\dfrac{1}{3}\right)+\left(-3\right)\right]+2.\left[\left(-\dfrac{1}{3}\right)+2\right]\\ \Leftrightarrow A=3.\left(-1-3\right)+2.\dfrac{5}{3}\\ \Leftrightarrow A=3.\left(-4\right)+2.\dfrac{5}{3}\\ \Leftrightarrow A=-12+\dfrac{10}{3}\\ \Leftrightarrow A=-\dfrac{26}{3}\)
Vậy \(A=-\dfrac{26}{3}\) tại \(x=-\dfrac{1}{3};y=-3\)