In a $\triangle ABC$,which of the following formulae are correct?
$I. r = 4R \sin \frac{A}{2} \sin \frac{B}{2} \sin \frac{C}{2}$
$II. r_1 = (s-a) \tan \frac{A}{2}$
$III. r_3 = \frac{\Delta}{s-c}$

  • A
    Only $I, II$
  • B
    Only $II, III$
  • C
    Only $I, III$
  • D
    $I, II, III$

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