In triangle \(ABC\), \(AB = AC\) and angle \(BAC = 40^\circ\). Find angle \(ABC\) and write down the mathematical name of this type of triangle.

Assessment: Mathematics 0580 | Paper 1 Mock 01 | Non-calculator (Core) Subject: Mathematics - 0580

Question 1 Report

In triangle \(ABC\), \(AB = AC\) and angle \(BAC = 40^\circ\).

Find angle \(ABC\) and write down the mathematical name of this type of triangle.

Answer Details

Since \(AB = AC\), triangle \(ABC\) is isosceles, so the two base angles \(ABC\) and \(ACB\) are equal. The angles of a triangle sum to \(180^\circ\), so the two equal angles share the remaining \(180 - 40 = 140^\circ\) between them.

\((180 - 40) \div 2\) [M1]

Angle \(ABC = 70^\circ\) [A1]

Isosceles [B1]

Read lesson note on Geometrical Terms (CIE)
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