Quick questions on The t-formula: rational expressions for $\sin \theta$ , $\cos \theta$ and $\tan \theta$ via $t = \tan(\theta/2)$

1short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is sign error after

1 - t^2

Show answer

\cos \theta = \frac{1 - t^2}{1 + t^2}

is positive when

|t| < 1

and negative when

|t| > 1

. Sketch a quick number line if unsure.

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