Question

How many terms of a.p 78,71,64....... are needed to give sum 468

Answer 1

Answer:

I Hope IT'S Helpful Plz make me brincly plz plz plz I need only 2 brincly plz plz plz make me brincly plz plz plz

Step-by-step explanation:

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

where Sn is sum of nterm in ap

a is first term and d is common difference

465=n/2{78.2+(n-1)(-7)}

930=n (156-7n+7)

930=163n-7n^2

7n^2-163n+930=0

now use quadratic formula for finding roots

n=10,186/14

hence only n=10 possible

t10=78-9x7=15

Answer 2

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

where Sn is sum of nterm in ap

a is first term and d is common difference

465=n/2{78.2+(n-1)(-7)}

930=n (156-7n+7)

930=163n-7n^2

7n^2-163n+930=0

now use quadratic formula for finding roots

n=10,186/14

hence only n=10 possible

t10=78-9x7=15