In $∆ABC$, $m∠C = 90°$, $AB = 10$ cm, and $\sin(A) = 0.5$. Without using a calculator, determine exact values for the following measures or ratios. 

1. $m∠A$  

   Hint (a):

   Refer to the Math Notes box from lesson 4.2.4 for help with inverse trigonometry.
   You may want to solve part (b) before part (a).

   Answer (a):

   $30°$

2. $BC$  

   Hint (b):

   $\text{Substitute }0.5 \text{ for sin}A \text{ in sin}A=\frac{BC}{10}.$

   Step (b):

   Then solve for $BC$.

3. $\cos(B)$  

   Hint (c):

   See hint for part (a).

4. $AC$  

   Hint (d):

   Use the information given and answer (c) to solve for $AC$ using the Pythagorean Theorem.