9x^2+25y^2=100
x^2/(100/9)+y^2/4=1
a=10/3,b=2
c^2=a^2-b^2=64/9
mx^2+y^2=8
x^2/(8/m)+y^2/8=1
所以有：8/m-8=64/9
m=9/17
或：8-8/m=64/9
m=9