|F2A|+|F2B|+|AB|=(|F2A|+|F1A|)+(|F2B|+|F1B|)=A到两个焦点的距离+B到两个焦点的距离=2倍长轴长度=2*(2√25)=20|AB|=20-12=8
f1a+f2a=f1b+f2b=10,因为f2a+f2b=12,所以ab=f1a+f1b=20-12=8
