Lời giải:
a)
$25+20x+4x^2=5^2+2.5.2x+(2x)^2=(5+2x)^2$
d)
$ab^2+\frac{1}{4}a^2b^4+1=(\frac{1}{2}ab^2)^2+2.\frac{1}{2}ab^2.1+1^2$
$=(\frac{1}{2}ab^2+1)^2$
b)
$a^2+9-6a=a^2-2.3a+3^2=(a-3)^2$
e)
$4x^4-4x^2+1=(2x^2)^2-2.2x^2+1^2=(2x^2-1)^2$
c)
$36a^2-60ab+25b^2=(6a)^2-2.6a.5b+(5b)^2=(6a-5b)^2$
f)
$9x^4+16y^6-24x^2y^3=(3x^2)^2-2.3x^2.4y^3+(4y^3)^2$
$=(3x^2-4y^3)^2$