12. (a) Given that \(\theta\) is small, show that \(2 \cos \theta + \sin \theta - 1 \approx 1 + \theta - \theta ^ { 2 }\).
(b) Hence, when \(\theta\) is small, show that $$\frac { 1 } { 2 \cos \theta + \sin \theta - 1 } \approx 1 + a \theta + b \theta ^ { 2 }$$ where \(a , b\) are constants to be found.
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