Question 29300: 0 = 5(x^3) + 10 + 10(x^2)
solve for x? or factor?
Answer by longjonsilver(2297)   (Show Source):
You can put this solution on YOUR website! Not too sure how to approach this apart from a numerical one... We have  . This does not factorise easily.
Approach is:
pick value of x
find the value of y
pick another value of x
when sign of y changes, we have "straddled" the solution, the root, the answer.
we then look at a more precise value of x and repeat the process.
So,
start with x=-1...  --> -1 + 2 + 2 --> +ve
now, try x = -2...  --> -8 + 8 + 2 --> +ve but getting closer to zero
now try x = -3...  --> -27 + 18 + 2 --> -ve
So the root lies between x=-2 and x=-3.
Now pick x=-2.5...  --> -ve, so the root lies between x=-2 and x=-2.5
So, pick x=-2.4...  --> -ve, Just. The root lies between x=-2 and x=-2.4
Pick x=-2.3...  --> +ve, so the root lies now between x=-2.3 and x=-2.4.
So now you try say x=-2.35 and work out the bounds of the root etc.
Looking at the graph, we do indeed see a solution between -2 and -3.
 is a closer look at the root.
jon
|
|
|
