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562.
The quotient rule
$\left(\dfrac{f}{g}\right)'=\dfrac{f'g-g'f}{g^2}$
563.
The quotient rule
$\left(\dfrac{f}{g}\right)'=\dfrac{f'g-g'f}{g^2}$
570.
Half Angle Formula of Sine
$\sin \dfrac{\alpha}{2} = \pm \sqrt{\dfrac{1-\cos\alpha}{2}}$