3x+5x+2=18的解细致一点

n=-2,n-2/n=(-1 )

x²-4x=2
x²-4x+4=6
(x-2)²=6
x-2=±√6
x1=2+√6, x2=2-√6

3x²+5x+1=0
3x²+5x=-1
x²+5x/3=-1/3
x²+5x/3+(5/6)²=-1/3+(5/6)²
(x-5/6)²=13/36
x-5/6=±(√13)/6
x1=(5+√13)/6 , x2=(5-√13)/6

8y-1=4y²
4y²-8y=-1
y²-2y=-1/4
y²-2y+1=-1/4+1
(y-1)²=3/4
y-1=±(√3)/2
y1=(2+√3)/2 , y2=(2-√3)/2

x²-5x+6=0
(x-2)(x-3)=0
x-2=0 或 x-3=0
x1=2, x2=3

原式=-3(x²-5x/3)+1
=-3(x²-5x/3+25/36-25/36)+1
=-3(x²-5x/3+25/36)+25/12+1
=-3(x-5/6)²+37/12
所以x=5/6时最大值是37/12