1. The problem statement, all variables and given/known data By direct substitution, show that equation (3) is a solution of the differential equation (2). 2. Relevant equations (2) (d^2 θ)/(dt^2 )=-g/l θ (Second derivative of θ(t)=-g/l θ.) (3) θ(t)=θ_0 cos(√(g/l) t) 3. The attempt at a solution I tried to integrate equation (2) and derive equation (3) but it didn't come out correctly.