Question

find the product of the following using the identity (x + a) (x + b) = x² + (a + b) x + ab.
i) (x + 4) (x + 7)
ii) (x + 6) ( x + 9)
iii) (x + 9) (x - 10)
iv) (x - 9) (x - 10)
v) ( x - 12) (x + 13)
vi) (x + 7) (x + 13) ​

Answer 1

Answer:

Formula

(x+a) (x+b) = x² + (a+b)x + ab

i) x = x

a = 4

b = 7

x² + (4+7)x + 4×7

x² + 11x + 28

ii) x = x

a = 6

b = 9

x² + (6+9)x + 6×9

x² + 15x + 54

iii) x = x

a = 9

b = -10

x² + (9-10)x + 9×-10

x² - 1x - 90

iv) x = x

a = -9

b = -10

x² + (-9-10)x + -9×-10

x² - 19x + 90

v) x = x

a = -12

b = 13

x² + (-12+13)x + -12×13

x² + (1)x + -156

vi) x = x

a = 7

b = 13

x² + (7+13)x + 7×13

x² + 20x + 91