Yes, you can use both.
Efficient and effective are somewhat different. Efficient (roughly) means "to accomplish a result with minimum effort or cost." Effective (roughly) means "to accomplish the desired result." Generally, being effective is highly valued (and being efficient is less valued). In certain contexts, such as a manufacturing plant, being efficient is highly valued.
(ineffective) - The little girl tried unsuccessfully to make a cake for her mother's birthday. Eventually, her father took her to the bakery to buy a cake.
(inefficient) - The teenage girl made a cake for her mother's birthday. She had made a cake only a few times before, so it took all day. [The teenage girl and the mother are both happy. The girl does not work in a bakery, so it is not very important to be efficient. In many jobs, being effective is required, and being (moderately) inefficient is tolerated. ]