Question

làm tính nhân

a) 3x(x+2) b) 4x(x-5) c) x(x+3) d) x(x+5)

e) (x+5)(x+1) f) (x+2)(x+3) g) (x+3)(x+4) h) (x+1)(x-2)

Answer 1

a) 3x(x + 2)

= 3x.x + 3x.2

= 3x² + 6x

b) 4x(x - 5)

= 4x.x + 4x.(-5)

= 4x² - 20x

c) x(x + 3)

= x.x + x.3

= x² + 3x

d) x(x + 5)

= x.x + x.5

= x² + 5x

e) (x + 5)(x + 1)

= x(x + 1) + 5(x + 1)

= x.x + x.1 + 5.x + 5.1

= x² + x + 5x + 5

= x² + 6x + 5

f) (x + 2)(x + 3)

= x(x + 3) + 2(x + 3)

= x.x + x.3 + 2.x + 2.3

= x² + 3x + 2x + 6

= x² + 5x + 6

g) (x + 3)(x + 4)

= x(x + 4) + 3(x + 4)

= x.x + x.4 + 3.x + 3.4

= x² + 4x + 3x + 12

= x² + 7x + 12

h) (x + 1)(x - 2)

= x(x - 2) + 1(x - 2)

= x.x + x.(-2) + 1.x + 1.(-2)

= x² - 2x + x - 2

= x² - x - 2