2a^2+1/ab+1/a(a-b)-10ac+25c^2=2a^2+(1/a)•[1/b+1/(a-b)]-10ac+25c^2=2a^2+(1/a)•[a/b(a-b)]-10ac+25c^2=2a^2+1/[b(a-b)]-10ac+25c^2又 b(a-b)≤(a/2)^2=a^2/4 ,则1/[b(a-b)]≥4/a^2则上式：≥2a^2+4/a...