A, B, C and D are points on a circle. Line PCQ is a tangent to the circle.
Line QE bisects angle AEC and is parallel to line CD.

  1. ((a))

    Show that EC = ED.
    Give a reason for each statement you make.

  2. ((b))

    Show that triangle AEF is similar to triangle QCF.
    Give a reason for each statement you make.

  3. ((c))

    Diameter AD = 28 cm and angle QCF = 61°.
    Calculate the area of segment CD.

    Answer ___ cm^2

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Worked solution

4((a))

1. Identify the two line segments as radii of the circle.

EE is the centre of the circle, and CC and DD lie on the circumference.

Therefore, ECEC and EDED are radii of the circle.

2. Use the property that radii of the same circle are equal.

All radii of the same circle are equal.

Hence, EC=EDEC = ED.

Answer

Since EE is the centre and CC and DD are points on the circle, ECEC and EDED are radii of the same circle.

Hence, EC=EDEC = ED.

4((c))

1. Find the radius of the circle.

Since ADAD is the diameter,
r=282=14 cm.r=\frac{28}{2}=14\text{ cm}.

2. Use the tangent-radius property to find $\angle FCE$.

Since QCQC is a tangent at CC, EC⊥QCEC \perp QC.

So
∠QCE=90∘.\angle QCE=90^\circ.
Given ∠QCF=61∘\angle QCF=61^\circ,
∠FCE=90∘−61∘=29∘.\angle FCE=90^\circ-61^\circ=29^\circ.

3. Find the central angle $\angle CED$ subtending chord $CD$.

In △ECF\triangle ECF, EC=EFEC=EF since both are radii.

Hence
∠EFC=∠FCE=29∘.\angle EFC=\angle FCE=29^\circ.
So
∠CEF=180∘−29∘−29∘=122∘.\angle CEF=180^\circ-29^\circ-29^\circ=122^\circ.
Since EF∥CDEF \parallel CD,
∠ECD=180∘−122∘=58∘.\angle ECD=180^\circ-122^\circ=58^\circ.
From part (a), EC=EDEC=ED, so △ECD\triangle ECD is isosceles.

Thus
∠EDC=58∘.\angle EDC=58^\circ.
Therefore
∠CED=180∘−58∘−58∘=64∘.\angle CED=180^\circ-58^\circ-58^\circ=64^\circ.

4. Calculate the area of the minor segment $CD$.

Area of segment CDCD
=area of sector CED−area of △CED.=\text{area of sector }CED-\text{area of }\triangle CED.

=64360π(14)2−12(14)(14)sin⁡64∘=\frac{64}{360}\pi(14)^2-\frac12(14)(14)\sin64^\circ

=21.386…=21.386\ldots

≈21.4 cm2.\approx 21.4\text{ cm}^2.

Answer

21.4 cm221.4\text{ cm}^2

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