Delta = $\frac{1}{2}$ab sin C = $\frac{1}{2}$bc sin A = $\frac{1}{2}$ca sin B (SAS form). Delta = sqrt(s(s-a)(s-b)(s-c)) (Heron's, SSS form). Delta = rs = $\frac{abc}{4R}$. Each formula suits different given information. The rs and $\frac{abc}{4R}$ forms connect area to inradius and circumradius.