The trigonometric expression is .

Let in the interval .

Let  in the interval .

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Difference formula of tangent function : .

Find .

Consider .

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From Pythagorean theorem,

The square of the hypotenuse is equal to sum the squares of the other two sides.

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Find .

Consider .

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From Pythagorean theorem,

.

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Substitute , .

, where and  .

, where and .