How can you tell if a trinomial is the square of a binomial?

The square of a binomial is always a trinomail since

(a+b) ^2=a^2+2ab+b^2 and so if you can write your trinomial as a^2+2ab+b^2 or a^2-2ab+b^2, it will be the square of a binomial specifically (a+b) ^2 and (a-b) ^2 respectively