5x²-6x+11
=5(x²-6x/5)+11
=5(x-3/5)²+11-9/5
=5(x-3/5)²+46/5;
∵(x-3/5)²≥0;
∴5x²-6x+11≥46/5;
所以是非负数
如果本题有什么不明白可以追问,