证明：-x²-6x+11的值不大于20.

1个回答

-x²-6x+11
=-x²-6x-9+20
=-(x-3)²+20
由于-(x-3)²≤0,所以-x²-6x-9+20≤20 ,
即-x²-6x+11的值不大于20.