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(a).

The expression is $\"\"$ .

From trigonometric functions $\"\"$ .

Rewrite the expression $\"\"$ .

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

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

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(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 $\"\"$ .