Activité 6 – Applications liées au calcul du périmètre

g)

Trouve la valeur de x (résous les équations).
3x = 45
x + 15 = 90
2x + 10 = 110
5x + 20 = 130
x + 15 – 15 = 90 – 15
2x + 10 – 10 = 110 – 10
5x + 20 – 20 = 130 – 20
x = 75
2x = 100
5x = 110
   
   
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3x = 45
x + 15 = 90
2x + 10 = 110
5x + 20 = 130
3 . 15 = 45 ?
75 + 15 = 90 ?
2 . 50 + 10 = 110 ?
5 . 22 + 20 = 130 ?
45 = 45 OK
90 = 90 OK
100 + 10 = 110 ?
110 + 20 = 130 ?
   
110 = 110 OK
130 = 130 OK
7x = 140
75 + x = 200
15 + 3x = 165
30 + 4x = 190
75 – 75 + x = 200 – 75
15 – 15 + 3x = 165 – 15
30 – 30 + 4x = 190 – 30
x = 125
3x = 150
4x = 160
   
   
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7x = 140
75 + x = 200
15 + 3x = 165
30 + 4x = 190
7 . 20 = 140 ?
75 + 125 = 200 ?
15 + 3 . 50 = 165 ?
30 + 4 . 40 = 190 ?
140 = 140 OK
200 = 200 OK
15 + 150 = 165 ?
30 + 160 = 190 ?
   
165 = 165 OK
190 = 190 OK
5x + 3x = 176
12x = 100 + 188
5x + 75 = 105
32 + 6x = 56
8x = 176
12x = 288
5x + 75 – 75 = 105 – 75
32 – 32 + 6x = 56 – 32
5x = 30
6x = 24
   
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8x = 176
12x = 100 + 188
5x + 75 = 105
32 + 6x = 56
8 . 22 = 176 ?
12 . 24 = 288 ?
5 . 6 + 75 = 105 ?
32 + 6 . 4 = 56 ?
176 = 176 OK
288 = 288 OK
30 + 75 = 105 ?
32 + 24 = 56 ?
   
105 = 105 OK
56 = 56 OK