Home » Ask & Discuss » Mathematics. » Analytical Geometry « Back to Discussion
Analytical Geometry
Comments (1)
venkat v.t
Scorching goIITian

Joined: 7 Aug 2007
Posts: 244
4 Nov 2007 21:28:53 IST
Like
0 people liked this
It is very useful theory to find intervals in which a function is positive or negative.
Eg) Find the values of x such that (x-2)(x-5)(x-8) greater than 0.
sol) First equate the given function to 0 and find roots.These are
called critical numbers.those are 2,5,8.
Mark 2,5,8 on the real line with ends -infinity and infinity.
Now we have -inf 2 5 8 inf on the real line.
write + in between last two ( 8 and inf),next -,next + .... alternatively
from right to left.
Now pick out the intervals having + signs.(since we need greater tha 0)
The answer is x belongs to (2,5)U(8,infinity)
+ indicates the curve above the real line and - indicates the curve below
the real line .Thats why it is called WAVY CURVE METHOD.
Reply











