a=2
d=4
S5 = 5/2 (2a+4d) = _____
d=4
S5 = 5/2 (2a+4d) = _____
2+6+18+54+162 = 242
or
a=2 r=3
sum(5) = a(r^5 - 1)/(r-1)
= 2(3^5 - 1)/2
= 242
I really gotta pay attention to GP vs AP!
or maybe check that d is really constant.
Thanks again, @mathhelper!
Sₙ = a(1 - rⁿ) / (1 - r),
where:
Sₙ is the sum of the first n terms,
a is the first term of the GP, and
r is the common ratio between consecutive terms.
In this case, the first term (a) is 2, and the second term can be obtained by multiplying the first term by the common ratio (r), which is 6/2 = 3. So, the second term is 2 * 3 = 6.
Now, let's calculate the sum:
S₅ = 2(1 - 3⁵) / (1 - 3)
Simplifying this expression, we have:
S₅ = 2(-242) / (-2)
S₅ = -484.
Therefore, the sum of the first five terms of the given GP 2, 6, 18 is -484.