Question

How many terms of A.P -6,-11\2,-5 are needed to give the sum_25

Answer 1

Answer:

n = 28

Step-by-step explanation:

a= -6

a2= -11/2

d= -11/2-(-6) , d= 1/2

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

25= n/2(2(-6) +(n-1)1/2

25 = n/2(-12+ n/2-1/2)

25= n/2(-12.5 + n/2)

25= -12.5n/2 + n^2/4

n^2/4-12.5n/2-25= 0 (finding the LCM , LCM=4)

n^2-25n-100= 0

using the formula;

-b+/-(b^2-4(a)(c))^1/2/2a = n

n= 28