$\"\"$

(a).

The expression is $\"\"$ .

Rewrite the above expression $\"\"$ .

From trigonometric functions $\"\"$ .

Rewrite the expression $\"\"$ .

Use the properties of inverse trigonometric function: $\"\"$ .

$\"\"$

The exact value of expression $\"\"$ .

$\"\"$

(b).

The expression is $\"\"$ .

From trigonometric functions $\"\"$ .

Rewrite the expression $\"\"$ .

Use the properties of inverse trigonometric function : $\"\"$ .

$\"\"$

The exact value of expression $\"\"$ .

$\"\"$

(a)The exact value of expression $\"\"$ .

(b)The exact value of expression $\"\"$ .