Answer:
c) BC/tan(20°)
Step-by-step explanation:
The mnemonic SOH CAH TOA can help you remember the relations between trig functions and angles. It tells you ...
Sin = Opposite/Hypotenuse
Cos = Adjacent/Hypotenuse
Tan = Opposite/Adjacent
In the case of the present triangle, these relations mean ...
sin(B) = AC/BC ⇒ AC = BCsin(70°)
cos(C) = AC/BC ⇒ AC = BCcos(20°)
tan(B) = AC/BA ⇒ AC = BAtan(70°)
tan(C) = BA/AC ⇒ AC = BA/tan(20°)
__
The answer choice that is not on this list is ...
c) BC/tan(20°) . . . . . . not equivalent to AC
_____
Additional comment
The interior angle at C is the supplement of the given angle 160°. These angles form a linear pair.
C = 180° -160° = 20°
The interior angle at B is the complement of the interior angle at C.
B = 90° -20° = 70°
