Using sigma notation, write down an expression for the series.
Mountaineers are climing a cliff, where B represents its base and T its top.
Let un=5n+3, for n∈ℤ+
(a). (i) Using sigma notation, write down an expression for u1+u2+u3+⋯+u20
∑k=120 (4k+1)
∑k=210 (4k+1)
∑k=1204k
4∑k=120 (k+1)
(ii) Find the value of the sum of the series.
A geometric sequence is defined by vn=5×3n-1, for n∈ℤ+.
(b). Find the value of the sum of the geometric series ∑k=110vk.