What is sqrt(2x^3)*sqrt(6x^2)*sqrt(10x)2x36x210x in simplified form?

1 Answer
Jan 28, 2017

sqrt(2x^3)*sqrt(6x^2)*sqrt(10x) = 2x^3sqrt(30)2x36x210x=2x330

Explanation:

Note that if a, b >= 0a,b0 then

sqrt(a)sqrt(b) = sqrt(ab)ab=ab

By extension, we find if a, b, c >= 0a,b,c0 then:

sqrt(a)sqrt(b)sqrt(c) = sqrt(ab)sqrt(c) = sqrt(abc)abc=abc=abc

Note also that if a>=0a0 then:

sqrt(a^2) = aa2=a

In our example, we will assume x >= 0x0 in order that all of the original square roots are well defined Real numbers.

So in our example:

sqrt(2x^3)*sqrt(6x^2)*sqrt(10x) = sqrt(2x^3*6x^2*10x)2x36x210x=2x36x210x

color(white)(sqrt(2x^3)*sqrt(6x^2)*sqrt(10x)) = sqrt(2x^3*2x^3*30)2x36x210x=2x32x330

color(white)(sqrt(2x^3)*sqrt(6x^2)*sqrt(10x)) = sqrt((2x^3)^2)sqrt(30)2x36x210x=(2x3)230

color(white)(sqrt(2x^3)*sqrt(6x^2)*sqrt(10x)) = 2x^3 sqrt(30)2x36x210x=2x330

Footnote

It seems to be a common error to assume that:

sqrt(x^2) = xx2=x

This does hold, but only if x >= 0x0.

If we want to cover the case x < 0x<0 too then we could write:

sqrt(x^2) = abs(x)x2=|x|

In the given example, we can deduce that the case x >= 0x0 is intended, since otherwise sqrt(2x^3)2x3 and sqrt(10x)10x could take imaginary values.