5ab²－｛2a²b－【3ab²－（4ab²－2a²b】｝
=5ab¬¬2-{2¬¬¬a2b-[3 ab¬¬2-4 ab²+2a²b]}
=5ab¬¬2-2¬¬¬a2b+(3 ab¬¬2-4 ab²+2a²b)
=5ab¬¬2-2¬¬¬a2b+2¬¬¬a2b- ab¬¬2
=7ab¬¬2-3 a2b
(x²－4y²－2z²)-(－4x²+2y²+3z²)*2
=9x²-8y²-8z²
原式=7-(x-y)-(x-y)²
=7-3-3²=-5