Asked by promise
1}
the first term of an AP is 2 and the common difference is 3.Find the sum of the first 11 terms. 2}The 2nd and 5th terms of a GP are -6 and 48 respectively.Find the sum of the first four terms
the first term of an AP is 2 and the common difference is 3.Find the sum of the first 11 terms. 2}The 2nd and 5th terms of a GP are -6 and 48 respectively.Find the sum of the first four terms
Answers
Answered by
Reiny
using our basic formulas
S(11) = (11/2)(4 + 10(3))
= 187
t2 = ar = -6
t5 = ar^4 = 48
divide them:
r^3 = 48/-6 = -8
r = -2
in ar = -6
a = 3
sum(4) = a(r^4 - 1)/(r-1)
= 3((-2)^4 - 1)/(-2-1)
= 3(15)/-3
= -15
check:
first 4 terms are:
3 , -6, 12, -24
add them to get -15
S(11) = (11/2)(4 + 10(3))
= 187
t2 = ar = -6
t5 = ar^4 = 48
divide them:
r^3 = 48/-6 = -8
r = -2
in ar = -6
a = 3
sum(4) = a(r^4 - 1)/(r-1)
= 3((-2)^4 - 1)/(-2-1)
= 3(15)/-3
= -15
check:
first 4 terms are:
3 , -6, 12, -24
add them to get -15
Answered by
bisola
15
Answered by
Joseph Davoty
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