Question

已知实数x，y满足x2+3x+y-3=0,则x+y的最大值为_____

Answer 1

由贺陆题目x²+3x+y-3=0可得禅行顷
x+y+x²+2x-3=0
x+y=-(x+1)²+4
当带敏x=-1时，x+y取最大值为4

Answer 2

令x+y=a
则y=a-x
所樱宽斗巧并以x²+3x+a-x-3=0
x²+2x+a-3=0
x是实数则△脊磨>=0
4-4a+12>=0
a<=8
所以x+y最大值是 8

Answer 3

y=3-x^2-3x
x+y=x+3-x^2-3x
=-x^2-2x+3
=-(x^2+2x-3)
=-((x+1)^2-1-3)
=-((x+1)^2-4)
=-(x+1)^2+4
x=-1,fmax=4

Answer 4

y=-x2-3x+3
x+y=x-x2-3x+3
=-x2-2x+3≥(-12-4)/(-4)=4
上面的做法厅败升是对枯戚的，但是算扮老错了……

Answer 5

满足x2+3x+y-3=0 确定这些没打错