Answer:
sin A or cos C
Step-by-step explanation:
Assuming that the length of BC is 4cm (it looks like a 6, sort of):
Looking at Angle A, the side labeled 4 is OPPOSITE angle A, and AC is the hypotenuse. The trig ratio that involves the opposite side and the hypotenuse is sine.
sin A = (opposite) / (hypotenuse) = 4 / 8.
Looking at angle C, the side labeled 4 is ADJACENT ("next to") angle C. The trig ratio involving the adjacent side and the hypotenuse is cosine.
cos C = (adjacent) / (hypotenuse) = 4 / 8.
