x²-x-5/4
=(4x²-4x+1-6)/4
=[(2x-1)²-6]/4
=(1/4)×(2x-1+√6)×(2x-1-√6)
9x²-6x-y²+4y-3
=9x²-6x+1-(y²-4y+4)
=(3x-1)²-(y-2)²
=(3x-1+y-2)(3x-1-y+2)
=(3x+y-3)(3x-y+1)已知m+n=12,则y=mn的最大值是？嘿嘿，再帮忙看看~因为m+n=12,所以m＝12－n则y＝mn ＝n(12-n) ＝-(n^2 -12n+36-36) ＝-(n-6)^2 +36所以当n=m=6时，y有最大值为36