He surveyed his homework with a complacent smile, knowing he would get an A.
Complacent= pleased, especially with oneself, advantages or situationsThe girl was complacent with her performance knowing she will win the competition for sure.
complex sentence (a sentence composed of at least one main clause and one subordinate clause)
The student was complacent in changing his behavior.
smug, self-satisfied, contented, satisfied, serene, unconcerned