Q：
Let y=-x/(x^2-2x+4), where x is real. a)Find the range of values of y for all real values of x. b)hence,find the value of x such that the value of y is maximum.
Sol：
a) yx^2+(1-2y)x+4y = 0
delta >= 0
(1-2y)^2 - 16y^2 >= 0
(1-6y)(1+2y) >= 0
-1/2 <= y<= 1/6
b) sub. y = 1/6
x^2 + 4x + 4 = 0
x = -2
