2（x²-3y²）²+24x²y²
=2[(x²-3y²)²+12x²y²] 完全平方化出来
=2(x^4-6x²y²+9y^4+12x²y²)
=2(x^4+6x²y²+9y^4) 完全平方
=2(x²+3y²)²