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Given: 0; -1; 1; 6; 14; .. - NSC Mathematics - Question 2 - 2016 - Paper 1

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Given: 0; -1; 1; 6; 14; ... 2.1.1 Show that this sequence has a constant second difference. 2.1.2 Write down the next term of the sequence. 2.1.3 Determine an exp... show full transcript

Worked Solution & Example Answer:Given: 0; -1; 1; 6; 14; .. - NSC Mathematics - Question 2 - 2016 - Paper 1

Step 1

Show that this sequence has a constant second difference.

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Answer

To show that the sequence has a constant second difference, we first calculate the first and second differences:

  • First Differences:

    • ( -1 - 0 = -1 )
    • ( 1 - (-1) = 2 )
    • ( 6 - 1 = 5 )
    • ( 14 - 6 = 8 )

    First differences: ( -1, 2, 5, 8 )

  • Second Differences:

    • ( 2 - (-1) = 3 )
    • ( 5 - 2 = 3 )
    • ( 8 - 5 = 3 )

    Second differences: ( 3, 3, 3 )

Since the second differences are constant (equal to 3), the sequence has a constant second difference.

Step 2

Write down the next term of the sequence.

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Answer

From the first differences, we see a pattern. The last first difference is 8, so the next first difference will be ( 8 + 3 = 11 ).

Thus, the next term can be calculated as follows: [ 14 + 11 = 25 ]

Therefore, the next term of the sequence is 25.

Step 3

Determine an expression for the nth term of the sequence.

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Answer

Given that the second difference is constant, we can express the nth term as: [ T_n = a n^2 + b n + c ]

We can calculate coefficients a, b, and c using the known terms:

  1. For n = 1: ( T_1 = 0 ) => ( a + b + c = 0 )
  2. For n = 2: ( T_2 = -1 ) => ( 4a + 2b + c = -1 )
  3. For n = 3: ( T_3 = 1 ) => ( 9a + 3b + c = 1 )

Solving these equations, we find: [ a = \frac{3}{2}, b = -\frac{11}{2}, c = 4 ]

Thus, the nth term is: [ T_n = \frac{3}{2}n^2 - \frac{11}{2}n + 4 ]

Step 4

Calculate the 30th term.

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Answer

Using the expression for the nth term: [ T_{30} = \frac{3}{2}(30^2) - \frac{11}{2}(30) + 4 ] Calculating further: [ T_{30} = \frac{3}{2}(900) - \frac{11}{2}(30) + 4 ] [ = 1350 - 165 + 4 ] [ = 1189 ]

Thus, the 30th term is 1189.

Step 5

Prove that a = 6 and b = 20.

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Answer

From the series: [ a + 13 + b + 27 + ... ] Using the information given:

  1. The sum of first two terms is: [ a + 13 = 6 + 13 \Rightarrow a = 6 ]
  2. For b, we see: [ b + 27 = 20 + 27 \Rightarrow b = 20 ]

Thus, it is proven that a = 6 and b = 20.

Step 6

Determine which term of the series will be equal to 230.

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Answer

To find the term equal to 230: [ S_n = a + (n-1)d ] where ( a = 6, d = b + 13 - 6 = 20 - 6 = 14 ) Set this equal to 230: [ 6 + (n-1) * 14 = 230 ] [ (n-1) * 14 = 224 ] [ n-1 = 16 \Rightarrow n = 17 ]

Thus, the 17th term of the series is 230.

Step 7

(1 - k/5) + (1 - k^2/5) + (1 - k^3/5) + ... converge?

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Answer

The series converges if the terms approach zero as ( n \to \infty ).

We can use the convergence test: [ 1 - \frac{k}{5}, ; \left(1 - \frac{k^2}{5}\right), ; \left(1 - \frac{k^3}{5}\right) ] will converge if: [ |1 - \frac{k}{5}| < 1 \Rightarrow |k| < 10 ]

Thus, the series converges for ( k < 10 ).

Step 8

Determine the sum of the first 40 terms of the series, to the nearest integer.

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Answer

Using the formula for the sum of the first n terms: [ S_n = \frac{n}{2} (a + l) ] where ( a = 16 ) and ( l = a + (n-1)d ) for the arithmetic series. Calculating:

  1. Find d: [ d = 3 - 16 = -13 ]
  2. Find l for n = 40: [ l = 16 + (40-1)(-13) = 16 - 507 = -491 ]
  3. Thus the sum S_40 is: [ S_{40} = \frac{40}{2} (16 - 491) = 20 * (-475) = -9500 ]

Therefore, the sum of the first 40 terms is -9500.

Step 9

Write the series: 16 + 8 + 4 + 2 + ... in the form \( \sum_{k} T_k \).

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Answer

The series can be written as: [ T_k = 16 \cdot (\frac{1}{2})^{k-1} ] Thus: [ S = \sum_{k=1}^{\infty} T_k = \sum_{k=1}^{\infty} 16 \cdot (\frac{1}{2})^{k-1} ]

Step 10

Determine S_0 of the series in QUESTION 2.4.2.

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Answer

To determine ( S_0 ): This series converges to: [ S_0 = \frac{a}{1 - r} ; ext{where} , a = 16, r = \frac{1}{2} ] Therefore: [ S_0 = \frac{16}{1 - \frac{1}{2}} = \frac{16}{\frac{1}{2}} = 32 ]

Hence, ( S_0 = 32 ).

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