Ta có:
\(\dfrac{SAMN}{SABC}\) \(=\) \(\dfrac{AM}{AB}\) . \(\dfrac{AN}{AC}\) \(=\) \(\dfrac{3}{5}\) . \(\dfrac{1}{2}\) \(=\) \(\dfrac{3}{10}\)
\(SABC =\) \(\dfrac{10}{3}\) \(SAMN=\) \(\dfrac{10}{3}\) . \(36\) \(=\) \(120 cm2\)
\(SBMNC = SABC - SAMN = 120 - 36 = 84 cm2\)
Đáp số: \(84cm2\)