2條math條/口\

1) For the equation 2x^3 + 4x^2 - 3x + 6 = 0, we can re-arrange it to:
2(x^3 + 2x^2 -x +2) -x +2 = 0
x^3 + 2x^2 -x + 2 = (x -2)/2. = x/2 - 1.
That means the intersecting point of
y= x^3 + 2x^2 -x +2 and
y= x/2 -1
will be the solution to the equation. from the graph provided, the answer is A(-2.9).
2)
f(x) = k is a horizontal line. The question is what is the range of value k such that the horizontal line will cut the graph at 3 distinct point. From the graph, it can be seen that if the horizontal is below y=2 and above y=1 will cut at 3 distinct points. Therefore, the answer is k less than 2 and greater than 1, that is A.
3)
Let x^2 = u, therefore, the equation becomes u^2 -8u -105 = 0
(u+7)(u-15) = 0
therefore, u= -7 or 15. that is x^2 = -7 or 15.
-7 is rejected, so x^2 = 15 , x= +/- sqrt15.

2008-07-08 22:38:20 補充：
Answer is D for Q.3.