Question

The common difference of an A.P is -2 find its sum if first term is 100 and last term is -10 PLZ PLZ PLZ ANSWER ME FAST ​

Answer 1

l = a + (n-1)d

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

n-1 = -110/-2 = 55

n = 56

Sn = (n/2)(a+ l)

S56 = 56/2( 100 - 10) = 2520

Answer 2

Plz refer to the attachment.