Question

The common difference of AP is -2 find its sum if first term is hundred and the last term is -10

Answer 1

Given ÷

a=100

d=-2

an=-10

To find ÷

Sn= ?

Solution÷

an=a+(n-1)d

-10=100+(n-1)-2

-10-100=2n-2

-110+2=2n

-108=2n

-108/2=n

-54=n

Now find Sn

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

Sn=-54/2{2*100+(-54-1)-2}

Sn=-27{200+(-55)-2}

Sn=-27{200+110}

Sn=-27{310}

Sn=(-8370)

Ans.....

Hope its helps u all ❤️☺️