BECE Mathematics 2025 Paper

Concept:The interior angles of a triangle add up to $180^\circ$, so third angle $= 180^\circ -$ (sum of the other two).Solution:Add the two given angles: $(3x - 10) + (4x + 20)$Collect $x$ terms: $3x + 4x = 7x$; collect numbers: $-10 + 20 = 10$Sum $= 7x + 10$Third angle $= 180 - (7x + 10) = 180 - 7x - 10$$= (170 - 7x)^\circ$Key point: The minus sign in front of the bracket applies to both terms: $-(7x + 10) = -7x - 10$.Answer:Option A ($(170 - 7x)^\circ$)