Posted by WINSTON on .
x(6x+1)<15
can some one explain the problem and answer to me step by step please.. I missing the process

math 
Steve,
x(6x+1) < 15
6x^2 + x  15 < 0
now you have a parabola. You need to find where it crosses the xaxis, and between those two points, it will lie below the xaxis.
(2x3)(3x+5) < 0
so, the roots are at x = 5/3 and 3/2
Between those two values, the parabola lies below the xaxis.
As a check, let's try the original conditions.
x(6x+1) < 15
at x = 5/3, x(6x+1) = 15
at x = 3/2, x(6x+1) = 15
Now check something in between, say x = 1,0,1
f(x) = 5,0,7 all < 15.
How about a few outside 5/3 < x < 3/2 ?
f(2) = 22 > 15
f(2) = 26 > 15
Take a look here:
http://www.wolframalpha.com/input/?i=x%286x%2B1%29+%3C+15 
math 
herp_derp,
Initial Problem
x(6x + 1) < 15
Simplify left side.
6x^2 + x < 15
Move 15 to left side.
6x^2 + x  15 < 0
Factor.
(2x  3)(3x + 5) < 0
Now, x MUST be BETWEEN the LESSER value and the GREATER value. (it is between because this is a "LESS THAN" inequality)
5/3 < x < 3/2