In the given figure, ∠AMN = ∠MBC = 76°. If a, b and c are the lengths of AM, MB and BC respectively then express the length of MN in terms of a, b and c.
In ΔAMN and ΔABC
∠AMN = ∠ABC = 76° (Given)
∠A = ∠A (common)
By AA Similarity criterion, ΔAMN ~ Δ ABC
If two triangles are similar, then the ratio or the their corresponding sides are proportional