Question

How many terms of the AP -10,-7,-4,-1,.............must be added to get the sum -104?

pls do this fasttttttstttt

Answer 1

The value of n is complex

Explanation:

The sequence is an arithmetic sequence

Given

First term a = -10

common diff d = -7-(-10) = -4-(-7) = 3

Sn = -104

get the number of terms n using the formula

Sn = n/2[2a+(n-1)d]

-104 = n/2[2(-10)+(n-1)(3)]

-104 = n/2[-20+3n-3]

-208 = n{3n-23}

-208 = 3n²-23n

3n²-23n+208 = 0

Factorize

n = 23±√23²+4(3)(208)/2(3)

n = 23±√529-2496/6

Since the value of n is a complex number, hence the value of n does not exist