Calculate the exact value of the expression [[$ \sqrt {1 – a^2} $]], when

a) [[$ a = \displaystyle\frac {1} {2} $]].

Take a picture of your answer and return it to the submission folder.

b) [[$ a = \displaystyle\frac {\sqrt {3}} {2} $]].

Answer: The value of the expression is .

(Source: Finnish matriculation exam, autumn 1987)