text: square root of 5x times square root of x minus 4 times square root of 5?   your phrasing makes the question unclear (what goes where?) so i'll just go through the different possibilities.  one is this:   sq(5x)*sq(x-4)*sq(5)  you can multiply together things in square roots.  let's do this:  sq(5(5x)(x-4)= sq(25x(x-4))= sq(25x^2-100x)   another possibility is this:  sq(5x)*sq(x)-4sq(5)=  bring the x out of sq(5x), by making it sq(x) (because you can take out things that are multiplied in square roots, but make sure they are still under a square root sign!)  sq(5)*sq(x)*sq(x)-4sq(5).  sq(x)*sq(x)=x.  we are multiply two square roots, so bring the x's under the same one.  multiply them, we get x^2.  the square root of x^2 is x.  x(sq(5))-4sq(5)=sq(5)(x-4)  there's your answer, if that was indeed the way i should have interpreted the question.  hope this helps.