## burhan101 2 years ago Restriction for logs

1. burhan101

|dw:1358467325462:dw|

2. burhan101

Now how do i find the restriction(s) for this ? :S

3. slaaibak

The thing in the bracket may not be less or equal to zero.

4. burhan101

x>-5, x>2 ?

5. slaaibak

yeah :)

6. burhan101

it's only supposed to be x>2

7. burhan101

i dont understand why

8. slaaibak

because the x has to satisfy both x>-5 and x>2, but since the has to be greater than 2, it can't fall between -5 and 2, because then the equation would be undefined

9. slaaibak

Think about it this way: The two restrictions must be met. Meaning, the number must be greater than 2 AND it must be greater than -5. But, if it is greater than 2, it is greater than -5! So, the greater than -5 is dominated by the greater than 2 restriction. Therefore the only restriction is greater than 2

10. burhan101

Ohhhhh, helps !

11. burhan101

but cant there be more than one restriction ? :S

12. slaaibak

There can. for instance, it it was log(-x + 7) + log(x+2), the restrictions would be -x + 7 > 0 AND x + 2 > 0 so, it's x< 7 AND x> -2 which reduces to: -2 < x < 7