The figure below is not drawn to scale. ABE is an equilateral triangle and BCD is an isosceles triangle. ABC and BDF are straight lines and AC // EF. ∠EBD = 90° and ∠BED = 43°.

  1. (a)

    Find ∠CBF.

  2. (b)

    Find ∠BDC.

  3. (c)

    Find ∠EDF.

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Worked solution

16(a)

1. Find $\angle ABE$ using the properties of an equilateral triangle.

Since triangle ABEABE is equilateral,
∠ABE=60∘\angle ABE = 60^\circ

2. Find $\angle CBF$ using vertically opposite angles.

Since ABCABC and FBDFBD are straight lines, ∠CBF\angle CBF and ∠ABD\angle ABD are vertically opposite angles.
∠ABD=∠ABE+∠EBD\angle ABD = \angle ABE + \angle EBD
∠ABD=60∘+90∘=150∘\angle ABD = 60^\circ + 90^\circ = 150^\circ
Therefore, ∠CBF=∠ABD=150∘\angle CBF = \angle ABD = 150^\circ

Answer

150∘150^\circ

16(c)

1. Find $\angle EDB$ using the sum of angles in $\triangle EBD$

In △EBD\triangle EBD, the sum of angles is 180∘180^\circ.
∠EDB=180∘−∠EBD−∠BED\angle EDB = 180^\circ - \angle EBD - \angle BED
∠EDB=180∘−90∘−43∘=47∘\angle EDB = 180^\circ - 90^\circ - 43^\circ = 47^\circ

2. Find $\angle EDF$ using angles on a straight line

Since BDFBDF is a straight line, ∠EDF\angle EDF and ∠EDB\angle EDB are supplementary.
∠EDF=180∘−∠EDB\angle EDF = 180^\circ - \angle EDB
∠EDF=180∘−47∘=133∘\angle EDF = 180^\circ - 47^\circ = 133^\circ

Answer

133∘133^\circ

AI analysis — may contain mistakes.

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