因为a-2b/a+2b=5,所以a+2b/a-2b=1/5
3(a-2b)/a+2b + (a+2b)/5(a-2b)
=3×5+1/5×(a+2b/a-2b)
=15+1/5×1/5
=15+1/25
=375/25+1/25
=376/25