What is the domain for (x^2-8x)^(1/4)?

2012-09-20 10:33 pm
Is it (-inf,inf)?

回答 (2)

2012-09-20 10:52 pm
✔ 最佳答案
Hello

Raising to 1/4 means take the square root of the square root.

You cannot take the square root of a negative number, it is not defined.

So, x² - 8x must be ≥ 0.

(x)(x - 8) ≥ 0

Make a short table

Between -inf and 0, x is negative. Over 0, it is positive
Between -inf and 8, x - 8 is negative. Over 8, it is positive

So, up to 0 both factors are negative ==> the product is positive
Between 0 and 8, x is positive, but x-8 negative ==> the product is negative
Over 8, both factors are positive ==> the product is positive

The function is defined when x ≤ 0 and when x ≥ 8.

Domain in interval notation : (-inf , 0] U [8, + inf)

Hope it helps

Bye !
2012-09-21 5:34 am
yes-- all real numbers will work


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