Hello ,Niva

It's preety simple if you didn't understanding from triangle then you can remember like that, the axis with which resultant makes angle that will be cos and other will be sine , there is no option to upload anything so still you didn't get I will try it by taking and instance ,  suppose X and Y-axis okky,now suppose resultant making and angle of 45° with x-axis , here it make angle with x-axis so x-axis will be cos component and y axis will be sin component .

Hope this will help you!!

Feel free to ask more queries