Find the sum S9 of the first 9 terms of the geometric sequence 1, −0.5, 0.25, …
Sequences & series worksheet with answers
1.Easy
a₁ = 1r = −0.5n = 9
S9 =
2.Easy
Find the sum S of the infinite series Σk=0∞ 12·(−2/3)ᵏ.
a = 12r = −2/3k₀ = 0
S =
3.Medium
Apply the ratio test to Σk=1∞ 3ᵏ·k!/kᵏ. Find L = lim |ak+1/ak|.
ak = 3ᵏ·k!/kᵏ
L =
4.Medium
Find the radius of convergence R of the power series Σk=1∞ k²·3ᵏ·(x + 1)ᵏ.
Σ k²·3ᵏ·(x + 1)ᵏx₀ = −1
R =
5.Hard
Use the Maclaurin polynomial of degree 4 of f(x) = 1/(1 − 2x) to approximate f(0.25). Give P₄(0.25).
f(x) = 1/(1 − 2x)n = 4x = 0.25
P₄(0.25) =
6.Hard
f(x) = eˣ is approximated by its Maclaurin polynomial of degree 5 at x = 0.3. Use the Lagrange error bound M·|x|ⁿ⁺¹/(n + 1)! with M = e0.3 = 1.35 to find the largest possible error |R₅|.
f(x) = eˣn = 5x = 0.3M = 1.35
|R₅| =
Answer key
- 1. S9 = 0.668
- 2. S = 7.2
- 3. L = 1.104
- 4. R = 0.3333
- 5. P₄(0.25) = 1.938
- 6. |R₅| = 1.367 × 10⁻⁶
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