已知2a的3次方+m次方b的5次方-9a的4次方b的n次方+1=7a的4次方b的5次方
2a^3+mb^5-9a^4b^n+1=7a^4b^5
3+m=4 5=n+1
m=1 n=4
(-2m+n)的n次方
=(-2*1+4)^4
=2^4
=16