Felix was asked whether the following equation is an identity: (x²+1)²=(x²-1)²+(2x)² He performed the following steps: (x=²+1)²
Step 1 x⁴+x²+x²+1
Step 2 x⁴+2x²+1
Step 3 x⁴+2x²+1-2x²+2x²
Step 4 (x⁴-2x²+1)+4x²
Step 5 (x²-1)²+(2x)²
For this reason, Felix stated that the equation is a true identity. Is Felix correct? If not, in which step did he make a mistake?
