3x19^2+6x19x21+3x21^2
=3x(19^2+2x19x21+21^2)
=3x(19+21)^2
=3x40^2
=3x1600
=4800
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解原渣耐式=3*19^2+2*3*19*21+3*21^2
=3*(如简春咐并19+21)^2
=3*40^2
=3*1600
=4800
3x19^2+6x19x21+3x21^2
=3(19^2+2x19x21+21^2)
=3(19+21)^2
=3x40^2
=3x1600
=4800
3x19^2+6x19x21+3x21^2
=3(19^2+2x19x21+21^2)
=3(19+21)^2
=4800