Sagot :
A(x) = (4x + 1)² - (6x - 11)²
1. Développement
A(x) = 16x² + 8x + 1 -(36x² - 132x + 121)=
A(x) = 16x² + 8x + 1 - 36x² + 132x - 121 =
A(x) = - 20x² + 140x - 120
2. Factorisation
Du type a² - b² = (a-b)(a+b)
A(x) = [(4x + 1) - (6x - 11)] [(4x + 1) + (6x - 11)]
A(x) = (4x + 1 -6x + 11) (4x + 1 + 6x - 11)
A(x) = (-2x + 12)(10x - 10)
3. Démontrer
A(x) = - 20(x -7/2)² + 125
A(x) = -20(x² - 7x + 49/4) + 125
A(x) = -20x² + 140x - 245 + 125
A(x) = - 20x² + 140x - 120
On retrouve bien la forme développée
4.
a) A(x) = 0
Forme factorisée
(-2x + 12)(10x - 10) = 0
Soit
-2x + 12 = 0
Et x = -12/-2 = 6
Soit
10x - 10 = 0
10x = 10
x = 1
x = {0;6}
b)
Forme développée
- 20x² + 140x - 120 = - 120
- 20x² + 140x = 0
x(-20x + 140) = 0
Soit x= 0
Soit - 20x + 140 =0
-20x = -140
x = 7
x = {0;7}
c) A(x) = - 20(x -7/2)² + 125
A(72) = - 20(72 -7/2)² + 125
A(72) = - 20(137/2)² + 125
A(72) = -20(18 769/4) + 125
A(72) = - 93 720
d)
A(x) = - 20x² + 140x - 120
A(0) = -120
1. Développement
A(x) = 16x² + 8x + 1 -(36x² - 132x + 121)=
A(x) = 16x² + 8x + 1 - 36x² + 132x - 121 =
A(x) = - 20x² + 140x - 120
2. Factorisation
Du type a² - b² = (a-b)(a+b)
A(x) = [(4x + 1) - (6x - 11)] [(4x + 1) + (6x - 11)]
A(x) = (4x + 1 -6x + 11) (4x + 1 + 6x - 11)
A(x) = (-2x + 12)(10x - 10)
3. Démontrer
A(x) = - 20(x -7/2)² + 125
A(x) = -20(x² - 7x + 49/4) + 125
A(x) = -20x² + 140x - 245 + 125
A(x) = - 20x² + 140x - 120
On retrouve bien la forme développée
4.
a) A(x) = 0
Forme factorisée
(-2x + 12)(10x - 10) = 0
Soit
-2x + 12 = 0
Et x = -12/-2 = 6
Soit
10x - 10 = 0
10x = 10
x = 1
x = {0;6}
b)
Forme développée
- 20x² + 140x - 120 = - 120
- 20x² + 140x = 0
x(-20x + 140) = 0
Soit x= 0
Soit - 20x + 140 =0
-20x = -140
x = 7
x = {0;7}
c) A(x) = - 20(x -7/2)² + 125
A(72) = - 20(72 -7/2)² + 125
A(72) = - 20(137/2)² + 125
A(72) = -20(18 769/4) + 125
A(72) = - 93 720
d)
A(x) = - 20x² + 140x - 120
A(0) = -120