3^x=4,3^y=5
则3^x*3^y*3^y=4*5*5
所以3^x+2y=100
3^4x+2y+1-（3^x+2y）^2
=(3^x)^4*(3^y)^2*3-100²
=4^4*5²*3-10000
=19200-10000
=9200