Find the sum S of the infinite series Σk=1∞ 18·(1/3)ᵏ.
Sequences & series worksheet with answers
1.Easy
a = 18r = 1/3k₀ = 1
S =
2.Easy
Find the sum S9 of the first 9 terms of the geometric sequence 1, 0.8, 0.64, …
a₁ = 1r = 0.8n = 9
S9 =
3.Medium
Apply the ratio test to Σk=1∞ kᵏ/(3ᵏ·k!). Find L = lim |ak+1/ak|.
ak = kᵏ/(3ᵏ·k!)
L =
4.Medium
Apply the ratio test to Σk=1∞ k²·3ᵏ/4ᵏ. Find L = lim |ak+1/ak|.
ak = k²·3ᵏ/4ᵏ
L =
5.Hard
f(x) = cos x is approximated at x = 2 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 1, find the smallest degree n that guarantees an error below 0.0005.
f(x) = cos xx = 2M = 1ε = 0.0005
n =
6.Hard
f(x) = ln(1 + x) is approximated by its Maclaurin polynomial of degree 4 at x = 0.5. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = 4! = 24 to find the largest possible error |R₄|.
f(x) = ln(1 + x)n = 4x = 0.5M = 24
|R₄| =
Answer key
- 1. S = 9
- 2. S9 = 4.329
- 3. L = 0.9061
- 4. L = 0.75
- 5. n = 9
- 6. |R₄| = 0.00625
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