how many terms of the series 2+4+6... amount to 42
Answers
Answered by
13
Answer:
6 terms
Step-by-step explanation:
First term, a = 2
difference of second and first term, d = 2
number of terms, n
formula for sum of A.P
Sn = n/2 [2a+(n-1)d]
42= n/2[2(2)+(n-1)2]
=n/2[4+2n-2]
=n/2[2n+2]
=n[n+1]
=n²+n
then by solving the quadratic eq.,
n²+n-42=0
n²-6n+7n-42=0
n(n-6)+7(n-6)=0
(n-6)(n+7)=0
n-6=0 or n+7=0
n=6 or n= -7
We will not consider the negative number of terms.
So, the answer is 6.
Answered by
0
Answer:
6 Term
Step-by-step explanation:
Sn = n/2 [2a+(n-1)d]
42= n/2[2(2)+(n-1)2]
42= n/2[4+2n-2]
42= n/2[2n+2]
42= n[n+1]
then by solving the quadratic eq., n?n(n-6)+7(n-6)=0
(n-6)(n+7)=0
n-6=0 or n+7=0
n=6 or n= -7
We will not consider the negative number of terms. So, the answer is 6.
Similar questions