# Domain of a radical function | Functions and their graphs | Algebra II | Khan Academy

2 min read

Domain of a Radical Function

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still confused as to why it is greater than or equal to…

God bless you Sir

How come Sal says that the domain is x >= 4. Shouldn't it also be x belongs to real numbers? Also, would the range be y >= 0, because the minimum value is zero? For a function, do we express the domain and range in terms of x and y, or do we just state them. Also, when is it that we have to put the domain and range in the curly brackets?

"plain vanilla principle root". I appreciate so much that you explain everything in clear, everyday language that non-math majors can understand! Plus a little humor thrown in! You are so educated, so knowledgeable, but you dont speak like a pompous know-it-all. Your explanations are life-savers for students who are otherwise drowning in "problem-based learning" & inadequate, poorly worded instruction at their schools. THANK YOU!!

@mystickybuns1 In this case, greater than or equal to is used because x can equal four, or anything greater than four. If x=4, than we would be taking the square root of zero, which is zero. Less than or equal to cannot be used here because x cannot equal anything less than four, as this would cause a negative number under the square root, giving us an imaginary number as an answer. To answer your question, the equation dictates whether or not to use greater than or equal to or less than/equalto

so for these types of problems do you only use greater than or equal to? never less than or equal to?

Second! !!

Thanks Sal