Let S=x+y and P=xy.
We are given:
S=x+y=x2+y2=x3+y3
Recall:
x2+y2=(x+y)2−2xy=S2−2P
x^3 + y^3 = (x + y)^3 - 3 x y (x + y) = S^3 - 3 P S
So, the system becomes:
1. S=S2−2P
2. S=S3−3PS
From (1):
S=S2−2P⟹S2−S−2P=0⟹2P=S2−S⟹P=2S2−S
From (2):
S=S3−3PS⟹S3−3PS−S=0⟹S3−S−3PS=0
Substitute P from above:
S3−S−3S⋅2S2−S=0
Multiply both sides by 2:
2S3−2S−3S(S2−S)=0
2S3−2S−3S3+3S2=0
(2S3−3S3)+(3S2)−2S=0
(−S3)+3S2−2S=0
S3−3S2+2S=0
S(S2−3S+2)=0
S(S−1)(S−2)=0
So the possible values for S are 0, 1, or 2.
Now, for each S, compute P:
- If S=0:
P=202−0=0
So x and y are roots of t2−0t+0=0⟹t2=0⟹t=0
So (x,y)=(0,0)
- If S=1:
P=212−1=0
So x and y are roots of t2−t=0⟹t(t−1)=0
So (x,y)=(0,1) and (1,0)
- If S=2:
P=222−2=24−2=1
So x and y are roots of t2−2t+1=0⟹(t−1)2=0⟹t=1
So (x,y)=(1,1)
Therefore, all solutions are:
(x,y)=(0,0), (0,1), (1,0), (1,1)