an AP 5,8,11 ... have 40 terms. find the last term . ans the sum of last 10 terms
Answers 2
Answer:
Last Term = 122
Sum of Last 10 terms = 1085
Step-by-step explanation:
a= 5
d= 3
n= 40
Thus,
an = a + (n-1)d
= 5 + (39) 3
5 +117
= 122
The last term of the AP is 122
For the sum of last terms,
Let A = 122 D = -3 n = 10
Thus
a10 = 122 + 9(-3)
= 122 -27
= 95 = L
Therefore sum of last 10 terms;
n/2 (A + L ) = 5 (122 + 95)
= 5 (217)
= 1085
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Author:
joelhanson
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20
Given,
An A.P 5, 8, 11, ... till 40 terms.
To Find,
The last term and the sum of the last 40 terms.
Solution,
In the given A.P
d = 8-5 = 3, a = 5
So,
a₄₀ = a+39d
a₄₀ = 5+39*3
a₄₀ = 5+117 = 122
Also,
we will find a₃₁ to get the sum of the last 10 terms.a₃₁ = a+30d = 5+30*3 = 5+90 = 95
Sum of last 10 terms = 10/2(95+122)
Sum of last 10 terms = 1085
Hence, the last term of the A.P is 122 and the sum of the last 10 terms of the A.P is 1085.
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Author:
sunshineqaz9
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5
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