2x²-3x≤2×+72x²-5x-7≤0x²-5x/2-7/2≤0x²-5x/2+25/16-81/16≤0(x-5/4)²-81/16≤0(x-5/4+9/4)(x-5/4-9/4)≤0(x+1)(x-7/2)≤0x1=-1x2=3.5解的集合为：[-1，3.5]
