(2)AD = A′D； ∠ADL =∠A′DL； Pull it at a right angle.

(3) △ a ′ an and △ a ′ dn are symmetrical.

(4)A′A = A′D； △ a ′ ad is an equilateral triangle.

(5) Because △ALD and △ a ′ LD are symmetric about LD.

So ad = a'd, ∠ADL =∠a'dl, ∠la'd =∠LAD = 90.

Because MN is the axis of symmetry

So A'A=A'D

So ad = a'd = a 'a.

So △ a ′ ad is an equilateral triangle.

So ∠a'da = 60.

So ∠ADL =∠A'DL = 30.

So a' l = 12ld.