# Thread: finding the domain of the function

1. ## finding the domain of the function

can someone please explain to me how to do this.

Find the value of a which will ensure that the domain of the function
f(x) = −9
√(a x+10) (-9 over sqrt(ax+10))
is the interval (−∞, 3), i.e. x < 3.

do you need to find the value of a, when x is 3? I'm a bit confused :S

2. The domain is $x<3$ which gives $ax+10<3a+10$

The function will be defined only if $ax+10>0$ (since square root of a negative term is not possible)

=> $3a+10>0$

=> $a>-\frac{10}{3}$