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These formulas explain how to add and subtract trigonometric functions (and their arguments). If you've got sum time, see what a difference these formulas will make for your trig toolkit.

If \(\sin\theta= \cos\theta\), find the value of \(\cos 2\theta\).

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Parth Lohomi**

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If \(A + B = 225^{\circ}\), find \((1+\tan A)(1+\tan B),\) where defined.

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Omkar Kulkarni**

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\[\large \frac {1}{\cos 80^\circ } - \frac {\sqrt 3}{\sin 80^\circ } = \ ? \]

**Hint:** How can we write the numerators in relation to common trig values?

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Gagan Raj**

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Pratik Shastri**

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\[ \sin^2 18^ \circ + \sin ^2 30 ^ \circ. \]

Which of the following is equal to the above expression?

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Calvin Lin**

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