Question

How many terms of ap-6 -11/2 -5 -9/2....Are needed give their sum - 25

Answer 1

Answer:Solved answer is 5

Step-by-step explanation:

Now we see that first term is (A)=(-6)

And by subtracting -6 from -11/2 we get -11/2 -(-6)

=-11/2 +6=1/2

Now by formula

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

We need sum as -25. So, Let term be =n

We get

- 25=N/2{-12+n/2-1/2}

-50=n(-25/2 + n/2)

Now multiplying 2 on both sides we get

-100=2n ✖ 1/2(-25+n)

-100= -25n+n*2

n*2-25n+100

N*2-20n-5n+100

(n-5)(n-20)

Now

N=5 or 20 clearly by solving

ANSWER IS 5