Remove all perfect squares from inside the square root 25x^4

The

the main rule:
for all value positive of a real  b,  √b²= b, and   √b*c=   √b * √c, if c is a real positive

let A=√25x^4,  we know that  25x^4=5² * x² * x² 
therefore,  
√25x^4= √5² * x² * x² =√5² √x² √x² = 5* x*x= 5x²

the final answer is A=√25x^4=5x²