Question

the sum of first 15 terms of the ap 10,6,2 is

Answer 1

Step-by-step explanation:

sum=n/2{ 2a + (n-1)d }

here a=10,d= -4 n=15

s= 15/2 { 2(10) + 14(-4) }

s = 15/2{ 20 - 56}

s= 15× -36

s= -540

Answer 2

Step-by-step explanation:

given that

10;6;2.......are in AP

a=10

d=a2-a1

=>6-10

=>-4

n=15

sum of first 15 terms =n/2(2a+(n-1)d)

=>15/2(2(10)+(15-1)-4)

=>15/2(20+(14)-4)

=>15/2(20+(-56))

=>15/2(20-56)

=>15/2(-36)

=>15(-18)

=>-270