In the figure below, EFGH is a rhombus and FGJK is a trapezium. EH and KF are straight lines. ∠KLH=55∘\angle KLH = 55^\circ and ∠HEF=110∘\angle HEF = 110^\circ

  1. (a)

    Find ∠KFH\angle KFH.

  2. (b)

    Find ∠HGJ\angle HGJ.

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Worked solution

12(a)

1. Find the angle ELF using vertically opposite angles or angles on a straight line.

Since K,L,FK, L, F are on a straight line, ∠ELF\angle ELF and ∠KLH\angle KLH are vertically opposite angles. Thus,
∠ELF=∠KLH=55∘\angle ELF = \angle KLH = 55^\circ

2. Find the angle EFL in triangle EFL.

In triangle EFLEFL, the sum of angles in a triangle is 180∘180^\circ. Given ∠HEF=110∘\angle HEF = 110^\circ (which is ∠LEF\angle LEF since LL lies on EHEH):
∠EFL=180∘−110∘−55∘=15∘\angle EFL = 180^\circ - 110^\circ - 55^\circ = 15^\circ

3. Find the diagonal angle EFH in the rhombus.

In rhombus EFGHEFGH, the diagonal FHFH bisects the interior angle ∠HEF\angle HEF (or we can use the isosceles triangle EFHEFH where EF=EHEF = EH):
∠EFH=180∘−110∘2=35∘\angle EFH = \frac{180^\circ - 110^\circ}{2} = 35^\circ

4. Calculate angle KFH.

Since LL lies on the line segment KFKF, the angle ∠KFH\angle KFH is the same as ∠LFH\angle LFH. Therefore:
∠KFH=∠EFH−∠EFL=35∘−15∘=20∘\angle KFH = \angle EFH - \angle EFL = 35^\circ - 15^\circ = 20^\circ

Answer

30∘30^\circ

AI analysis — may contain mistakes.

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