In the diagram, O is the centre of the circle. DOEFG and AEB are straight lines and GA is a tangent to the circle at A. Angle AGD = 32° and angle BCD = 106°.

  1. (a)

    angle GOA ,

    Answer ...°

  2. (b)

    angle BCF ,

    Answer ...°

  3. (c)

    angle BDA ,

    Answer ...°

  4. (d)

    angle DEA .

    Answer ...°

Work through it with AI →

It won't just hand you the answer — it asks where you're stuck.How the checker works

Worked solution

7(a)

1. Identify the right angle between the tangent and radius

Since GAGA is a tangent at AA and OAOA is a radius,
∠OAG=90∘.\angle OAG = 90^\circ.

2. Use the angle sum of triangle $AOG$ to find $\angle GOA$

Since D,O,E,F,GD,O,E,F,G are collinear, ∠AGO=∠AGD=32∘\angle AGO = \angle AGD = 32^\circ.

In △AOG\triangle AOG,
∠GOA=180∘−90∘−32∘=58∘.\angle GOA = 180^\circ - 90^\circ - 32^\circ = 58^\circ.

Answer

58∘58^\circ

7(b)

1. Identify the right angle subtended by diameter $DF$ at $C$

Since D,O,FD, O, F are collinear and OO is the centre, DFDF is a diameter of the circle.

Hence,
∠DCF=90∘\angle DCF = 90^\circ
(angle in a semicircle).

2. Subtract to find $\angle BCF$

Given
∠BCD=106∘,\angle BCD = 106^\circ,
and CFCF lies inside ∠BCD\angle BCD.

Therefore,
∠BCF=∠BCD−∠DCF\angle BCF = \angle BCD - \angle DCF
=106∘−90∘= 106^\circ - 90^\circ
=16∘.= 16^\circ.

Answer

16∘16^\circ

7(c)

1. Find the angle between chord $AD$ and radius $AO$

From part (a), ∠GOA=58∘\angle GOA=58^\circ.

Since D,O,GD,O,G are collinear,
∠AOD=180∘−58∘=122∘.\angle AOD=180^\circ-58^\circ=122^\circ.

In △AOD\triangle AOD, OA=ODOA=OD as radii, so
∠OAD=∠ODA=180∘−122∘2=29∘.\angle OAD=\angle ODA=\frac{180^\circ-122^\circ}{2}=29^\circ.

2. Use the cyclic quadrilateral and tangent-chord theorem to find $\angle BDA$

Since A,B,C,DA,B,C,D lie on the circle, opposite angles of cyclic quadrilateral ABCDABCD are supplementary:
∠BAD=180∘−106∘=74∘.\angle BAD=180^\circ-106^\circ=74^\circ.

Hence
∠BAO=∠BAD−∠OAD=74∘−29∘=45∘.\angle BAO=\angle BAD-\angle OAD=74^\circ-29^\circ=45^\circ.

Since GAGA is tangent at AA, GA⊥AOGA\perp AO, so the angle between tangent GAGA and chord ABAB is
∠GAB=90∘−45∘=45∘.\angle GAB=90^\circ-45^\circ=45^\circ.

By the tangent-chord theorem,
∠BDA=∠GAB=45∘.\angle BDA=\angle GAB=45^\circ.

Answer

45∘45^\circ

7(d)

1. Find $\angle DAE$ using the cyclic quadrilateral

Since A,E,BA,E,B are collinear, ∠DAE=∠DAB\angle DAE=\angle DAB.

In cyclic quadrilateral ABCDABCD,
∠DAB+∠BCD=180∘\angle DAB+\angle BCD=180^\circ
∠DAE=∠DAB=180∘−106∘=74∘.\angle DAE=\angle DAB=180^\circ-106^\circ=74^\circ.

2. Find $\angle ADE$ using the radius triangle $AOD$

From part (a), ∠GOA=58∘\angle GOA=58^\circ.

Since D,O,GD,O,G are collinear,
∠AOD=180∘−58∘=122∘.\angle AOD=180^\circ-58^\circ=122^\circ.

As OA=ODOA=OD, triangle AODAOD is isosceles, so
∠ADO=180∘−122∘2=29∘.\angle ADO=\frac{180^\circ-122^\circ}{2}=29^\circ.

Since D,O,ED,O,E are collinear,
∠ADE=29∘.\angle ADE=29^\circ.

3. Use the angle sum of triangle $ADE$ to find $\angle DEA$

In triangle ADEADE,
∠DEA=180∘−74∘−29∘=77∘.\angle DEA=180^\circ-74^\circ-29^\circ=77^\circ.

Answer

77∘77^\circ

AI analysis — may contain mistakes.

Worked this one out on paper? Snap your steps and Gigle's AI math checker will circle the step where it went wrong.

More questions on this topic

  1. 1A circle with centre O has a tangent XY at D. ∠ODC = 70°, ∠BCD = 120° and ∠ODA = 15°. Find ∠CDY. Find ∠DAB. Find ∠OBA. T…
  2. 2In the diagram, BA and BC are tangents to the circle with centre O. BO meets the circle at D, OA = 10 cm and BC = 28 cm.…
  3. 3The diagram shows a circle PQRST, with centre O. PV and RV are tangents to the circle and U is the intersection of PS an…
  4. 4A, B and C are points on the circle with centre O. Q and R are points on the circle with centre P. CSR and BSQ are tange…
  5. 5下列关于圆的叙述正确的有( ) ①圆内接四边形的对角互补; ②相等的圆周角所对的弧相等; ③正多边形内切圆的半径与正多边形的半径相等; ④圆内接平行四边形是矩形. A. 1个 B. 2个 C. 3个 D. 4个