Question

in an A.P., the first term is 25, n term is - 17 and the sun to first n terms is 60. find the common difference.

Answer 1

Answer:

Step-by-step explanation:

Sn=n/2(a+an)

60=n/2(25+(-17))

60=n/2(8)

60×2/8=n

n=15

now

an=a+(n-1)d

-17=25+(15-1)d

-17-25=14d

d=-42/14=-3

so,

n=15

d=-3

Answer 2

are you serious

ok let's see

let common difference be 'd'

first term=25

nth term=-17

first term+(n-1)d=-17.......eq1

sum of nth term=60

n/2{first term+nth term}=60

n(25-17)=120

n=120/8

n=15

putting value of n in eq 1

we get

25+14d=-17

d=-42/14

d=-3

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