cowboys93
Jul 8, 2009, 07:34 PM
The question says,Graph the function and determine the intervals for which f(x) is greater than or equal to than 0.
 
f(x)=4x+2
 
Help pllleaseee
Perito
Jul 8, 2009, 08:21 PM
You wrote f(x) = 4x +2.  What values of this are equal to zero?  How about
 
0 = 4x + 2? 
 
If you solve this for x, you'll see what value of x is zero.  You can then figure out what values of x make the function greater than zero.
 
Let me give you an example.  Let's say that you have the equation
 
f(x) = 17x - 34
 
We look at the equation
 
0 = 17x -34
17x = 34
x = 2
 
So we know that f(x) = 0 for x = 2.  What about x > 2?  Let's try x=3
 
f(3) = 17 * 3 - 34 = 17   yup > 0
 
You can show that for any x > 2, f(x) will be greater than 0.
 
What about x < 2?
 
f(1) = 17 * 1 -34 = -17
 
You can also show that for any x<2, f(x) will be less than zero.
 
Therefore, for this equation, the intervals for which f(x) >= 0 are x= 2 to x= infinity
 
You can also solve this equation
 
17x - 34 >= 0
 
17x >= 34
 
x >= 2
 
We haven't divided by any negative numbers, which would reverse the sign.  We've just proven what we saw, above.  You do the same thing for your equation:
 
f(x) = 4x+2 >= 0