=-9(x²-8x/9+16/81)+16/9-2
=-9(x-4/9)²-2/9
∵-9(x-4/9)²<=0
∴-9(x-4/9)²-2/9<0
∴）-9X的平方+8X-2的值恒小于0第一步怎么来的