# Domain

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• May 28th 2010, 07:51 PM
winsome
Domain
find the domain of -4sin(3x)
• May 28th 2010, 08:00 PM
papex
sin(x) is defined for all real numbers, so are sin(3x) and -4sin(3x)
• May 28th 2010, 08:07 PM
winsome
Quote:

Originally Posted by papex
sin(x) is defined for all real numbers, so are sin(3x) and -4sinsin(3x)

I want to find the domain of -4 sin (3x).
• May 29th 2010, 12:20 AM
Grandad
Hello winsome

Do you understand what is meant by the word domain of a function? It is the set of valid inputs to that function. For example, the domain of $\displaystyle \sqrt x$ is the set of non-negative numbers.

Now, as papex has said, $\displaystyle \sin x$, and therefore $\displaystyle \sin3x$ and $\displaystyle -4\sin 3x$, are defined for all values of $\displaystyle x$. In other words, the domain of these functions is the set of all real numbers.

There are various ways of writing this set. One is to use the symbol $\displaystyle \mathbb{R}$. Another is to use interval notation: $\displaystyle (-\infty, +\infty)$.

Grandad