document.write( "Question 173900: Umm...if someone please has the time to help me, I need to know how to find the domain of a function. The problems are like this:\r
\n" ); document.write( "\n" ); document.write( "squareroot of X^2-X-20\r
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Algebra.Com's Answer #128779 by solver91311(24713) $\"\"$ $\"About$

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The domain of a function is that set of values for which the function is defined. In your example, where you are taking the square root of something, that something cannot be negative. You need to examine the polynomial that forms your radicand and determine the interval, if any, where values of x in that interval would make the entire polynomial have a value that is less than zero.\r
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\n" ); document.write( "\n" ); document.write( "Hint: Factor the polynomial to find the roots of $\"X%5E2-X-20=0\"$ . These roots will give you endpoints of the excluded interval. Note that the vertex of the parabola described by $\"y=X%5E2-X-20\"$ is at $\"-%28-1%29%2F%282%2A1%29=1%2F2\"$ , so you will want to determine the sign of the function value at $\"1%2F2\"$ . That piece of information will tell you whether the interval between the roots is excluded from or included in the domain. The domain will then be all values NOT excluded. \n" ); document.write( "

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