由x²/4-y²/3=1知a=2,
因此|MF2|+|NF2|-|MN|
=|ME2|+|NF2|-(|MF1|+|NF1|)
=(|MF2|-|MF1|)+(|NF2|-|NF1|)
=2a+2a
=4a=8.