2x²-3x-1=2（x²-3/2x)-1=2(x²-3/2x+9/16)-1-9/8=2(x-3/4)²-17/8当x=3/4时,有最小值-17/84x²-12xy+10y²+4y+9=(4x²-12xy+9y²)+(y²+4y+4)+5=(2x-3y)²+(y+2)²+5...