Question

The algebraic expression of the sum of terms of an arithmetic sequence is n2+8n.Ths sum
of continuous terms starting from the first of this sequence is found to be 240.
a) Write second degree equation based on this statement.
b) The sum of how many terms is 240?​

Answer 1

Answer:

12

Step-by-step explanation:

We can express this as n²+8n = 240

n²+8n-240 = 0

Let n1, n2 be the roots of this equation. Using the formula to find roots of a quadratic equation,

n1, n2 = (-8±√(8²-(4*-240*1)))/(2*1) = (-8 ± √(64+960) )/2 = 12 and -20

We can ignore the negative root and hence n = 12.