Evaluate the expression 2n(n-1), when n =
= 3
A 11
B 12
C 17
D 18

The value of the expression is 12 ⇒ B

Step-by-step explanation:

Let us solve the question

∵ The expression is 2n(n - 1)

→ Simplify it at first by multiply 2n by the bracket (n - 1)

∵ 2n(n - 1) = 2n(n) - 2n(1)

∴ 2n(n - 1) = 2n² - 2n

∵ n = 3

→ Substitute n by 3 in the expression to find its value

∴ 2n² - 2n = 2(3)² - 2(3)

∴ 2n² - 2n = 2(9) - 6

∴ 2n² - 2n = 18 - 6

∴ 2n² - 2n = 12 ⇒ at n = 3

∴ The value of the expression is 12

see explanation

step-by-step explanation:

a

(6r + 7) + (13 + 7r) ( remove brackets and collect like terms )

= 6r + 7 + 13 + 7r

= 13r + 20

b

remove brackets and collect like terms

13 - r - 1 + r

= 12 - r

c

remove brackets and collect like terms

= - 8 - r + 2r - 4

= - 12 + r

d

remove brackets and collect like terms

= 7r - - - 6r

[-   - = - - = - ]

= r -