+9665 Firstly, k must be a square number(1, 4, 9, ... etc.)
Next, we will analyze the second term of the trinomial.
-20x = \(2\times 2x\times (\text{Something})\)
\((\text{Something})= -5\)
Next, we will find the square of that (Something).
\(\boxed{(-a)^2=a^2}\\ (-5)^2=5^2=25\)
Therefore k = 25.
4x^2 - 20x + 25 = \((2x)^2-2\times 2x \times (-5)+(-5)^2=(2x-5)^2\)
