3x^2-5x-12的最小值和-3x^2-5x-12的最大值,此时x分别得________

3x^2-5x-12=3(x^2-5/3x+25/36)-3×25/36-12=3(x-5/6)^2-169/12当x=5/6时3x^2-5x-12有最小值-169/12 -3x^2-5x-12=-3(x^2+5/3x+25/36)+3×25/36-12=-3(x+5/6)^2-119/12当x=-5/6时3x^2-5x-12有最大值-119/12...