Question

Which equation can be used to find the length of ? (10)sin(40o) = AC (10)cos(40o) = AC = AC = AC

Answer 1

the answer:
ABC is a right triangle.
according to the figure, the length AC is the opposite side relative to the angle 40°, 
for that, the main formula is 

sin40° = opposite side / hypotenuse

opposite side =AC, and hypotenuse = 10 in
 
therefore,  sin40° = AC  / 10, and then  AC = 10 sin40°
so for finding the value of AC, we can use   AC = 10 sin40°

look at the image for more explanation
 

Answer 2

The answer would be (10)sin(40 degrees)=AC.
Hope it helps!