GCSE Maths Practice: triangles-and-quadrilaterals

Question 5 of 10

This question calculates base angles in an isosceles triangle.

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\( \begin{array}{l}\text{An isosceles triangle has a top angle of } 100^\circ.\\ \text{Find the size of each base angle.}\end{array} \)

Choose one option:

Subtract top angle from 180° and divide by 2 for base angles.

An isosceles triangle has two equal sides and two equal base angles. The sum of all angles is always 180°. Given the top angle, the base angles can be calculated as (180° - top angle)/2. For example, top angle = 100° → base angles = (180 - 100)/2 = 40°. Understanding this principle helps solve triangle problems, identify triangle types, and apply geometric rules. Practicing labeling triangles and calculating missing angles reinforces reasoning and visualization skills, which are important for GCSE geometry. Real-life applications include design, construction, and architecture, where angle calculations are crucial. Repetition with different top angles improves speed and accuracy.