Question

[Linh Phương]

(y+3)³-(y+1)³=56

TÌM Y

Answer 1

[Nguyễn Lê Phước Thịnh]

\(\left(y+3\right)^3-\left(y+1\right)^3=56\)

\(\Leftrightarrow y^3+9y^2+27y+27-y^3-3y^2-3y-1=56\)

\(\Leftrightarrow6y^2+24y+26-56=0\)

\(\Leftrightarrow\left(y+5\right)\left(y-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}y=-5\\y=1\end{matrix}\right.\)

Answer 2

[Long Nguyễn Song Thiên]

\((y+3)^3 -(y+1)^3=56\\ \Leftrightarrow y^3+9y^2+27y+27-y^3-3y^2-3y-1=56\\ \Leftrightarrow 6y^2+24y-30=0 \Leftrightarrow x=1 \text{ hoặc } x=-5\)