Outside the middle school program / Inscribed and center angles 19 exercises (including 17 corrected)

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OABCDC60o AHMTC ABMOC ABCHOEC ABCOHC OCABH37oC 1. Angles and trigonometry E.801 Let C be a circle of center O and radius 5 cm . Points A , O , C are aligned. D is a point of C such that BDC =60 o . Determine the measure of seg-ment [ BC ] rounded to the nearest millimeter. E.2493 On the figure opposite the measures are not respected. Consider a circle C of di-ameter HA =9 cm . Let M be a point on the circle C such that MA =5.3 cm and T another point on the cir-cle C . 1 Justify that MAH is a right-angled triangle. 2 Calculate the measure, rounded to the nearest unit, of the angle MHA . 3 Determine the measure, rounded to the nearest unit, of the angle HTM . E.2647 The figure opposite is not full-scale. It is not required to be re-produced. C is a circle of center O and diameter [ AB ] such that AB = 6 cm . M is a point on the circle such that BM =4.8 cm . 1 Demonstrate that the tri-angle ABM is right-angled at M . 2 Calculate the measure of the angle ABM , rounded to the degree. 3 Deduce the measure of the angle AOM , rounded to the degree. E.4051 The figure below is not to be re-peated on the copy. It is not given in full size. A , B and C are three points on a circle C with center O . We know that AB =3 cm . The height AH measures 2.5 cm . The diameter [ AE ] is plotted. 1 What is the nature of the triangle ACE ? Justify the answer. 2 Explain why the angles ABC and AEC are equal. 3 Using the triangle ABH , calculate the exact value of sin ABH and deduce the measure of the angle AEC rounded to the degree. E.798 The figure opposite is not drawn to actual dimensions. The circle C has as its center the point O and its radius is 5 cm . The triangle ABC is in-scribed in the circle C and such that BOC =80 o . Note H the point of intersec-tion of the straight line ( AO ) with the circle C . 1 Show that the straight line ( AO ) is the perpendicular bisector of the segment [ BC ] . 2 Calculate the value of the angle OAB . Justify. 3 What is the nature of the triangle ABH ? Justify. 4 Calculate the length of [ BH ] . E.799 The figure opposite does not show the actual dimensions. Let C be a circle of center O and radius 5 km . A , B and C are three points on the cir-cle C such that BAC =37 o . H is the foot of the height from O in the triangle ABC . 1 a Determine the measure of the angle BOC . b Calculate the value of the angle OBC . 2 Calculate the length of segment [ BH ] rounded to the nearest decameter. https://chingmath.fr chapExoCorrec/801 sacados/801 OABCDC60o chapExoCorrec/2493 sacados/2493 AHMTC chapExoCorrec/2647 sacados/2647 Brevet 2007 ABMOC chapExoCorrec/4051 sacados/4051 Reims Septembre 2002 ABCHOEC chapExoCorrec/798 sacados/798 ABCOHC chapExoCorrec/799 sacados/799 OCABH37oC
CABCOHE OCNBAM80o25oC OMBAI20oC OIJKC E.5406 The figure below is not to be repeated on the copy. It is not given in full size. A , B and C are three points on a circle C (see fig-ure) . We know that AB =3 cm , the height [ AH ] measures 2.5 cm . We trace the diameter [ AE ] . 1 What is the nature of the triangle ACE ? Justify the answer. 2 Explain why the angles ABC and AEC are equal. 3 Using the triangle ABH , calculate the exact value of sin ABH and deduce the measure of the angle AEC rounded to the nearest degree. 2. Angles and isosceles triangles E.800 The points A , B , C , M and N belong to the cir-cle C of center O verify-ing the measures : AOB =80 o ; BNC =25 o 1 Calculate the mea-sure of AMB . 2 Calculate the mea-sure of each angle of triangle BOC . 3 Deduce the measure of each of the angles AOC and AMC . E.802 Let C be a circle of center O . A , B , M three points of the circle such that ABM =20 o . Let I be the middle of seg-ment [ AB ] . Calculate the value of the an-gle AOB . Justify. E.5405 The figure opposite is not full-scale ; we do not ask you to re-produce it. Consider a circle C with center O and diameter 8 cm . I and J are two diametrically opposed points. K is a point of C such that JK =4 cm . 1 a Specify the nature of the triangle OJK . Justify. b Deduce the measure of the angle JIK . Justify your answer. 2 a Specify the nature of the triangle IJK . Justify. b Give the measurement, to the nearest millimetre, of segment [ IK ] . 3 We call R the image of K by symmetry of axis ( IJ ) . Demonstrate that the quadrilateral ROKJ is a rhombus. 3. Angles and right-angled triangles E.4338 Consider the figure below, which is not full-scale. It is not necessary to redo the figure. https://chingmath.fr chapExoCorrec/5406 sacados/5406 Brevet de Reims Septembre 2002 CABCOHE chapExoCorrec/800 sacados/800 OCNBAM80o25oC chapExoCorrec/802 sacados/802 OMBAI20oC chapExoCorrec/5405 sacados/5405 OIJKC chapExoCorrec/4338 sacados/4338 Pondichery Avril 2011
ABDOMC75o ABCOHC(d ABDEC BDACC ABD is an isosceles tri-angle at A such that : ABD =75 o ; C is the circumscribed circle of the triangle ABD ; O is the center of the cir-cle C ; [ BM ] is a diameter of C . 1 What is the nature of the triangle BMD ? Justify the answer. 2 a Calculate the measure of the angle BAD . b Name an inscribed angle that intercepts the same arc of the circle C as the angle BMD . c Justify that the angle BMD measures 30 o . 3 We give : BD =5.6 cm ; BM =11.2 cm Calculate DM . Round the result to the nearest tenth. 4. Angles and thales E.805 The figure opposite is not made to actual dimensions. Let C be a circle of center O radius 6 cm . Points A and C are diametri-cally opposed. B is a point on the circle such that BC =3 cm . The segment [ BC ] measures 3 cm in length. The line ( d ) is perpendicular to ( BC ) passing through the point O . It intersects segment [ BC ] at H . 1 What is the nature of the triangle ABC ? Justify. 2 Determine the measure of the angle BAC . 3 a Determine the measure of the angle BOC . Justify b What is the nature of the triangle OBC ? Justify c Deduce the measure of the angle BOH d Justify the fact that : BH =1.5 cm . 4 Calculate the value of OH to the nearest millimetre. E.3928 On the figure opposite, which is not full-scale, we know that : ( C ) est a circle with center E dont the diameter [ AD ] mesure 9 cm . B is a point of circle C such that : AEB =46 o 1 Make the figure respecting the given dimensions. 2 Show that the triangle ABD is a right-angled triangle. 3 Justify that : ADB = 23 o . 4 Calculate the length AB and specify its value rounded to the hundredth of cm . 5 Draw the line parallel to the line ( AB ) passing through E . It intersects segment [ BD ] at point F . Place the point F . 6 Calculate the length EF and specify its value rounded to the tenth of cm . 5. Small and large bows E.2938 Consider a quadrilateral ABCD inscribed in a circle C . Show that the opposite angles, in the quadrilateral ABCD , are angles of supplementary mea-sures. Hint : use the eight angles formed by the intersection of the two diagonals of the quadrilat-eral. https://chingmath.fr ABDOMC75o chapExoCorrec/805 sacados/805 ABCOHC(d chapExoCorrec/3928 sacados/3928 Asie Juin 2009 ABDEC chapExoCorrec/2938 sacados/2938 BDACC
CABCIJKM 304050ABCFigureno1ABCDE(DE==(ACFigureno2ABCEFigureno340o50o Figure 1Figure 2ABCE60o20oABCDE(AC==(DE Figure 3Figure 4ABC5;5cm4;5cm7;5cmBCDEest un losangede centreAABCDE E.2939 In the plane, consider any triangle ABC and its circumscribing circle C ; the point M is any point on the circle C ; let I , J , K be the orthogonal projects of the point M onto the straight lines ( AC ) , ( BC ) , ( AB ) , respec-tively. The aim of this exercise is to show that the points I , J , K are aligned. 1 a Establish that the points I and J belong to the circle of diameter [ MC ] . b Justify that the angles IJM and ICM have the same measure. c Deduce the relationship : ACM =180 IJM 2 a Justify that the points B , J , K , M are cocyclic; Specify the nature of the circle to which they belong. b Establish the equality: ABM =180 MJK To demonstrate this relationship, we’ll use the diago-nals of the quadrilateral JMBK 3 The points A , B , C , M are cocyclic (as in question 2 b ) ; we accept the following relationship : ABM = 180 ACM Deduce that the points I , J , K are aligned The straight line passing through these three points is called Simson’s straight line. 6. A little of everything E.2492 Demonstrate, for each of the three figures below, that the triangle ABC is a right-angled triangle using the information provided. E.3274 Complete the table below : https://chingmath.fr chapExoCorrec/2939 sacados/2939 CABCIJKM chapExoCorrec/2492 sacados/2492 Groupe est - juin 2002 - 4 points 304050ABCFigureno1ABCDE(DE==(ACFigureno2ABCEFigureno340o50o chapExoCorrec/3274 sacados/3274 Brevet juin 2010 - 6 points Figure 1Figure 2ABCE60o20oABCDE(AC==(DE Figure 3Figure 4ABC5;5cm4;5cm7;5cmBCDEest un losangede centreAABCDE
CCOPABQ6cm4cm ABCOM5cm Figure 1 Figure 2 Figure 3 Figure 4 Is triangle ABC a right triangle in A ? Yes No Yes No Yes No Yes No Number(s) of the property or prop-erties that prove this List of properties: 1 If a quadrilateral is a rhombus, then its diagonals have the same midpoint and are perpendicular. 2 If two lines are perpendicular to the same third line, then they are parallel to each other. 3 If, in a triangle, the square of the length of the longest side is not equal to the sum of the squares of the lengths of the other two sides, then the triangle is not a right triangle. 4 In a triangle, the sum of the measures of the three angles is equal to 180 o . 5 If two lines are parallel and a third line is perpendicular to one of them, then it is perpendicular to the other. 6 If a quadrilateral has four sides of equal length, then it is a rhombus. 7 If two angles inscribed in a circle intercept the same arc, then they have the same measure. 8 If in a triangle, the square of the length of the longest side is equal to the sum of the squares of the lengths of the other sides, then this triangle is a right triangle and the right angle is the angle opposite the longest side. 7. Unclassified financial years E.5989 The circle C has center O and radius 4 cm . Note [ PQ ] a diameter of the circle C . We construct the circle C of center P and radius 6 cm . Note A the point of intersec-tion of the circle C and the segment [ PQ ] and B one of the of the intersection points of the two circles C and C . The aim of the exercise is to determine an approximate value for the area of the shaded part. We will work with rounded measurements : 1 a Determine the area of the triangle BPQ . b Deduce the area of triangle POB . 2 a Determine the measure, rounded to a tenth of a de-gree, of the angle PQB . b Deduce the area, rounded to the tenth of cm 2 , of the angular sector of the circle C defined by the arc PB . 3 Deduce a measure, rounded to the tenth of cm 2 , of the shaded part. E.6058 Consider an isosceles triangle ABC at A such that angle BAC measures 50 o and AB is equal to 5 cm . Let O be the center of the cir-cle circumscribed around trian-gle ABC . The line ( OA ) inter-sects this circle, denoted ( C ) , at another point M . 1 What is the measure of an-gle BAM ? No justification is required. 2 What is the nature of triangle BAM ? Justify your answer. 3 Calculate the length AM and round it to the nearest tenth. 4 The line ( BO ) intersects the circle C at another point K . What is the measure of angle BKC ? Justify your answer. https://chingmath.fr sacados/5989 CCOPABQ6cm4cm sacados/6058 ABCOM5cm