Grade 8 / Other 9 exercises (including 3 corrected)

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1. The Pythagorean triplets E.1951 The triplet a ; b ; c ) of integers is said to be Pythagorean if : a 2 + b 2 = c 2 Here, the study of several ways to obtain Pythagorean triplets : 1 The Pythagorean formula : a Complete the table below : n 2 n +1 2 n 2 +2 n 2 n 2 +2 n +1 1 2 5 b Show, using the calculator, that for : n = 1 ; n = 2 ; n = 5 The triplets of integers : 2 n +1 ; n 2 +2 n ; 2 n 2 +2 n +1 are Pythagorean triplets. 2 Plato’s formula : a Complete the table below : n 2 n n 2 1 n 2 +1 1 2 6 b Show, using the calculator, that for : n = 1 ; n = 2 ; n = 6 the triplets of integers 2 n ; n 2 1 ; n 2 +1 are Pythagorean triplets. 3 Eculides’ formula : a Complete the table below : m n 2 mn m 2 n 2 m 2 + n 2 2 1 3 2 5 2 b Show, using the calculator, that the three inte-ger triplets 2 mn ; m 2 n 2 ; m 2 + n 2 are Pythagorean triplets. E.1345 1 Using double distributivity, show the following equality: (2 n 2 + 2 n )(2 n 2 + 2 n ) = 4 n 4 + 8 n 3 + 4 n 2 2 Give the expanded and reduced form of the following ex-pression : (2 n + 1) 2 (use double distributivity with (2 n +1)(2 n +1) ) 3 Establish the following equality: (2 n 2 + 2 n + 1) 2 = 4 n 4 + 8 n 3 + 8 n 2 + 4 n + 1 4 Show that the triplet 2 n +1 ; 2 n 2 +2 n ; 2 n 2 +2 n +1 is a Pythagorean triplet for any positive integer n . 2. The square roots E.1956 Definition: (provisional) Let a be a positive number. We call the square root of the number a the positive number such that its square is equal to a . Let’s start by showing that there is only one number that changes the diagram below : 1 Suppose there are two positive numbers a and b such that a 2 = b 2 . a Expand and reduce the expression : ( a + b )( a b ) . b What can we say about the two numbers x and( y that satisfy : x × y = 0 c We can deduce that : a b =0 . We have just shown the uniqueness of the square root. The previous definition becomes : Definition: Let a be a positive number. We call the square root of the number a the unique positive number such that its square is equal to a . We denote this number a Study of some algebraic properties: 2 a Calculate the square of the number 5 × 3 . b Compare 5 × 3 and 15 . c Using the same method, show the following equality for any positive number a and b : a × b = a × b 3 a Simplify the following calculation: 7 3 × 7 3 b Complete the following sentence : 7 3 is a number whose square is . . . . . . c Similarly, show that for all positive numbers a and b , with b =0 , we have a b = a b Some simplifications of fractions : 4 a What number squared equals 5 2 ? b Deduce the value of 5 2 . c Similarly, for any positive real number a , determine the value of a 2 . 5 a Establish the equality 50=5 2 by squaring each https://chingmath.fr sacados/1951 sacados/1345 sacados/1956
EFG member. (Establish the equality by using the equality) b Determine two integers a and b such that : 50 = a 2 × b c Using the questions 2 et 4 , establish the equality in another way: 50 = 5 2 3. The GPS system and triangulation E.1344 The only instruments allowed are a ruler and a compass : 1 In the figure below, place point M satisfying the follow-ing conditions : EM = 5 cm ; FM = 4 cm ; GM = 7 cm 2 Are two points sufficient to perfectly locate the position of a third point in the plane? Justify your answer. Note: la Triangulation by measuring distances (or trilateration) allows us to determine the exact position of a point by knowing its distance from other points. On the plane, on the surface of the earth, at least three points are needed to locate a point exactly. E.1346 Note: Quartz is a mineral used to regulate the timing of all modern watches. Quartz is obtained from silica, which has piezoelectric properties discovered by Pierre and Jacques Curie in 1880. Here is a brief description of the piezoelec-tric effect : When subjected to mechanical stress (pressure, stretch-ing) , it develops an electric field ; When subjected to an electric field, quartz undergoes deformation. The first property is used in particular in gas lighters : when a button is pressed, the gas lighter creates an electric arc. The second property is used in mini-motors (nanotechnol-ogy) . In watches, an electronic system allows these two properties to alternate and stabilizes this alternation at a frequency of 32 768 Hz : the quartz will thus vibrate regularly 32 768 times per second. Let us assume four objects with internal clocks set to the same time: 3 transmitters ( E , F , G ) and 1 receiver ( R ) . It is assumed that the waves emitted by the 3 transmitters propagate at the speed of light, which is 3 × 10 8 m = s (in fact 299 792 458 m = s ) . The receiver R is set to the same time, so it can measure the time taken by the signal from each transmitter. Here is one of its readings : Time of parcours the signal Distance actual (in cm ) Distance to the scale (in cm ) from E to R 0 ; 0004 s from F to R 0 ; 001 s from G to R 0 ; 0017 s 1 Calculate the distance between point M and each of the receivers. 2 Here are points E , F , G shown on a map at scale 1 = 6 000 000 https://chingmath.fr chapExoCorrec/1344 sacados/1344 EFG sacados/1346
EFG S1S2O RSEFGHIRSEFGHIPremier casSecond cas SREFGHISREFGHITroisième casQuatrième cas RST Place point R (construction lines must remain visible) . Note: the GPS positioning system (Global Positioning Sys-tem) consists of 29 satellites in orbit. Each of these satellites carries an atomic clock (see box) and sends a signal at reg-ular intervals including the satellite’s position and the date and time the message was transmitted. Quartz clock systems have a margin of error of a few sec-onds per year, while atomic clocks, based on the vibrational properties of the cesium atom, have an accuracy of a few seconds per million years. An observer O located on Earth receiving signals from two satel-lites and able to measure the dis-tance between themselves and these satellites. This is insuf-ficient to determine their exact position : the intersection of two spheres can be a circle. For a GPS receiver to function properly, it is necessary to receive signals from at least 4 satellites to determine its po-sition on Earth. E.1347 Here are four figures representing the same points R and S and a contour line between these two points. 1 Complete the following table : In each case, complete the following table : RF SF RF SF RI SI RI SI 1 o 2 o 3 o 4 o Note: Each of these curves represents the set of points such that the difference in distance between them and points R and S is constant. These curves are called hyperbolas, and points R and S are called the foci of the hyperbola. These curves are used in particular to determine the epicen-ter of an earthquake : we do not know the time of emission of the seismic waves, but we can measure the difference in the arrival time of the signal between two receivers. In this case, three receivers are also needed to determine the exact position of the emission source. 3 Below is a cross-section of the earth, where points R , S , and T represent receivers placed on the earth’s surface : We know that : https://chingmath.fr EFG S1S2O sacados/1347 RSEFGHIRSEFGHIPremier casSecond cas SREFGHISREFGHITroisième casQuatrième cas RST
sssssssssssST AgdeSèteMontpellierNîmesBalarucD31D31A927kmBalarucA990kmNîmesD3154kmNîmesD31A9Balaruc14km 123ABCDEFNombrededemi-journéesTarifATarifB183521640345 the seismic waves arrived at receivers R and S at the same time while the signal arrived Δ=4 s seconds earlier at re-ceiver S than at receiver T . Determine the exact location of the epicenter F of the earthquake. 4. Unclassified exercises E.6336 Paul wants to go from Agde to Montpel-lier. He has two choices : either he takes the highway A9 , or he takes the departmental road D31 . Here, diagrammed, is the information he retrieves from a map : 1 He estimates that he is averaging 110 km = h on the highway and 75 km = h on county roads. Which route should he take to get to the city of Montpe-lier the fastest? 2 On the same route, Adeline leaves at 9 h using the county road while juliette leaves at 9 h 15 . That she is the driver who will arrive in Montpelier the soonest. E.8945 An association offers a variety of activities to keep children occupied during the school vaca-tions. Several rates are offered : Rate A : 8 e per half day; Rate B : a membership of 30 e entitling the member to a discounted rate of 5 e per half day. A spreadsheet file has been prepared to calculate the cost to be paid based on the number of half days of activities for each of the proposed rates : Questions 1 , 2 , 4 , and 5 do not require justification. 1 Complete this table. 2 Find from the following answers the formula that was entered in cell B3 before stretching it to the right : a =8 × B1 b =30 × B1+5 c =5 × B1+30 × BA d =30+5 × B1 e =35 https://chingmath.fr sssssssssssST sacados/6336 AgdeSèteMontpellierNîmesBalarucD31D31A927kmBalarucA990kmNîmesD3154kmNîmesD31A9Balaruc14km chapExoCorrec/8945 sacados/8945 123ABCDEFNombrededemi-journéesTarifATarifB183521640345
quandest cliquécachermettre la taille du stylo à1e∑acer toutaller à x:0y:0Rectangleajouter40àxajouter-20àyrépéter5foisde∏nir rectanglestylo en position d’écritures’orienter à90degrésavancer de40tournerde90degrésavancer de20tournerde90degrésrépéter2foisrelever le stylo ajouter1à la taille du stylo E.8898 We want to make a frieze com-posed of rectangles. To do this, we wrote the program below : Recall that the instruction ˇ orient to 90 ı is to orient horizon-tally to the right. In this exercise, no justification is required. 1 What are the coordinates of the starting point of the plot? 2 How many rectangles are drawn by the main script? 3 Draw the figure obtained with the main script freehand. 4 a Without modifying the main script, we obtained the figure below composed of rectangles of length 40 pix-els and width 20 pixels. Propose a modification to the block ˇ rectangle ı that would result in this figure. b Where can we then add the instruction : in the main script to get the figure below? https://chingmath.fr chapExoCorrec/8898 sacados/8898 quandest cliquécachermettre la taille du stylo à1e∑acer toutaller à x:0y:0Rectangleajouter40àxajouter-20àyrépéter5foisde∏nir rectanglestylo en position d’écritures’orienter à90degrésavancer de40tournerde90degrésavancer de20tournerde90degrésrépéter2foisrelever le stylo ajouter1à la taille du stylo