1.当x＜0时 f（x)=x(1+x) = x² + x = x² + x + 1/4 -1/4 = (x +1/2)² - 1/4
为顶点（-1/2,-1/4）开口向上的抛物线.
f(x)是定义在R上的奇函数,x >0时,为顶点（1/2,1/4）开口向下的抛物线：f(x) = -(x -1/2)² + 1/4
= -x² + x = x(1 - x)
图像自己画.
2.x^2+3=4x,x² -4x + 3 = 0,(x-3)(x-1) = 0
x = 3 或x = 1
B有两个元素1,3
若A∪B=B,则A有下列可能：
a.空集,p²-4q ＜0
b.只含元素1,x²+px+q = 0 有相同的根1,(x-1)² = x² -2x + 1 = 0,p = -2,q = 1
c.只含元素3,x²+px+q = 0 有相同的根3,(x-3)² = x² -6x + 9 = 0,p = -6,q =9
d.含元素1,3:x²+px+q = 0 有根1,3,(x-3)(x-1) = x² -4x + 3 =0,p = -4,q = 3
3.f(x) = (2x-1)/(x+2) = (2x + 4 -5)/(x+2) = 2 - 5/(x+2)
x属于[3,5]时,x+2随x增加而增加,5/(x+2)随x增加而减小；2 - 5/(x+2)随x增加而增加.
x = 3时,f(x)取[3,5]内的最小值=2 - 5/(3+2) = 1
x = 5时,f(x)取[3,5]内的最大值=2 - 5/(5+2) = 9/7
x属于[3,5]时,f(x)值域:[1,9/7]