Question

Tìm x,y : 3x = 2y và (x+y)³ - (x-y)³ = 126

Answer 1

3x=2y

=>\(\dfrac{x}{2}=\dfrac{y}{3}=k\)

=>x=2k; y=3k

\(\left(x+y\right)^3-\left(x-y\right)^3=126\)

=>\(\left(2k+3k\right)^3-\left(2k-3k\right)^3=126\)

=>\(\left(5k\right)^3-\left(-k\right)^3=126\)

=>\(126k^3=126\)

=>k³=1

=>k=1

=>\(x=2\cdot1=2;y=3\cdot1=3\)