Answer:
The length of BC is needed because it is the side opposite ∠A.
Step-by-step explanation:
Given the right angles triangle as shown in the attachment, we can get sin(A) without using Pythagoras theorem. Instead we will use SOH CAH TOA trigonometry identity.
According to SOH:
Sin(A) = Opposite/Hypotenuse
Sin(A) = |BC|/|AB|
Opposite side of the triangle is the side facing ∠A.
Based on the formula, we will need to get the opposite side of the triangle which is length BC for us to be able to determine sinA since the hypotenuse is given.
