inner angle
The total is 180, ∠ C = 70, ∠ ADE+∠ B = 1 10.
De: ∠a=∠ade
So ae=ed, and the triangle aed is
isosceles triangle
And because point f is the midpoint of ad.
So ef divides ad vertically in two.
I hope I can help you. If you don't understand, ask again.