Chapter 5 - Polynomials and Polynomial Functions - 5-2 Polynomials, Linear Factors, and Zeros - Practice and Problem-Solving Exercises - Page 295: 64

$x^2+5x+4=(x+4)(x+1)$

The leading coefficieint is 1. Thus, to factor the trinomial, look for the factors of the constant term (4) whose sum is equal to the coefficient of the middle term (5). Note that $4=4(1) \text{ and } 4+1=5$. Thus, the factored form of the trinomial is $(x+4)(x+1).$