√(a²-2a-8)+|2a²-3a-20|=0,则 a²-2a-8=0,2a²-3a-20=0,由a²-2a-8=0 (a-4)(a+2)=0得a=4或a=-2由2a²-3a-20=0(2a+5)(a-4)=0,得 a=4或-2.5所以a=4