Solutions 
A Perfect Square Trinomial is the product of two binomials. Both the binomials are same. When you multiply an algebraic expression with two terms to itself, you will get a three-term expression called a perfect square trinomial. A perfect square trinomial is one that factors into two identical factors. The general forms of perfect square trinomial are = 
(ax - b)² = (ax)² - 2axb + b² and (ax + b)²= (ax)² + 2axb + b²
Calculations 
αx²+βx+c
The variable α = 1 for ease
Take the variable b and half it then square that
to make c = number
x²+2x+c
variable α = 1 
variable β = 2 
2 ÷ 2=1
1² = 1 
x²+2x+1
(x+1)² 
In conclusion the number (1) should be added to the expression to turn it into a perfect square trinomial .