Question

write the first five terms for each of the following a) the first term is 7, and the common difference is -3 b) a=-12, d=5

Answer 1

a)

a = 7

d = -3

a1 = a = 7

a2 = a+d = 7-3 = 4

a3 = a2+d = 4-3 = 1

a4 = a3+d = 1-3 = -2

a5 = a4+d = -2-3 = -5

AP is 7, 4, 1, -2, -5

b)

a = -12

d = 5

a1 = a = -12

a2 = a+d = -12+5 = -7

a3 = a2+d = -7+5 =-2

a4 = a3+d = -2+5 =3

a5 = a4+d = 3+5 = 8

AP is -12, -7, -2, 3, 8

Answer 2

Answer:

Step-by-step explanation:

use your formula

$a = 5, d = 2 , n = ? , sum(n) = 480$

$(n/2)(10 + 2(n-1)) = 480$

$n(8 + 2n) = 960$

$8n + 2n^2 = 960$

$n^2 + 4n - 480 = 0$

$(n+24)(n-20) = 0$

$n = -24 or n = 20$ , but n must be a whole number

the sum of $20 terms$ would be $480$

check:

sum $(20) = (20/2)(10 + 2(19)) = 480$

=$AP is -12, -7, -2, 3, 8$

hope it helps

:)