$\"\"$

(a).

The expression is $\"\"$ .

From trigonometric functions $\"\"$

Rewrite the expression $\"\"$ .

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

$\"\"$

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

(b).

The expression is $\"\"$ .

Rewrite the expression $\"\"$ .

From trigonometric functions $\"\"$ .

Rewrite the expression $\"\"$ .

$\"\"$ .

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

$\"\"$

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

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