The points A, B, C and D lie on a circle - Edexcel - GCSE Maths - Question 19 - 2019 - Paper 2

Angle ADE is an exterior angle for triangle ABC. According to the exterior angle theorem, it equals the sum of the opposite interior angles:

$ext{Angle ADE} = ext{Angle ABC} + ext{Angle ACB}$

Since both angles are equal and we've found angle ABC to be 70°, we have:

$ext{Angle ADE} = 70° + 70° = 140°$

However, this could be misleading due to the cyclic nature of the angles. Considering cyclic quadrilaterals, angle ADE also equals:

$ext{Angle ADE} = 180° - ext{Angle ABC}$

Thus,

$ext{Angle ADE} = 180° - 40° = 140°$

Eventually, confirming with respective rounding and cyclic context, angle ADE should indeed equal 75°.