Why do you doubt? Which part did you do deliberately incorrectly?
It is a simple enough question. You worked the problem, but somehow wondered if you managed the correct answer. This causes me to wonder which part you did incorrectly on purpose. If you did the whole thing correctly, and on purpose, I have to wonder why you doubt your result.
Did you draw a right triangle? Did you designate and angle of interest? Did you label the legs of the triangle "1" and "4"? Did you calculate the length of the hypotenuse? Did you then determine the correct value of the cosine of the designated angle? Answer these questions and gain confidence in your work.
You don't seem to want to learn. Answer my questions and you will learn.
Show how you worked the problem. Demonstrate ALL intermediate steps. Let's see why you don't get to the end with confidence.
In the case you offered, let's see if I can reproduce your thinking... 2 + 2 = 4, I'm trying to be funny and I'm a little annoyed, so I'll deliberately say the result is "5". See, now that's clear where you deliberately made an error and it's clear why you should not have confidence in this result. Let's try the given problem statement and see where it leads.