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vredina [299]
3 years ago
14

A. [4 marks]

Mathematics
1 answer:
storchak [24]3 years ago
7 0

The value of d is -2

Step-by-step explanation:

The nth term of the arithmetic sequence is u_{n}=u_{1}+(n-1)d , where

  • u_{1} is the first term
  • d is the common difference between each 2 consecutive terms

The nth term of the geometric sequence is u_{n}=u_{1}r^{n-1} , where

  • u_{1} is the first term
  • r is the common ratio between each two consecutive terms r=\frac{u_{2}}{u_{1}}=\frac{u_{3}}{u_{2}}

∵ u_{1} of an arithmetic sequence is 1

∵ The common difference is d, where d ≠ 0

∵ u_{2} , u_{3} , u_{6} are the first 3 terms of a geometric sequence

∵ u_{2} = 1 + (2 - 1)d

∴ u_{2} = 1 + d

∵ u_{3} = 1 + (3 - 1)d

∴ u_{2} = 1 + 2d

∵ u_{6} = 1 + (6 - 1)d

∴ u_{2} = 1 + 5d

∴ The first 3 terms of the geometric sequence are (1 + d) , (1 + 2d) ,

   (1 + 5d)

∵ The common ratio in the geometric sequence is r=\frac{u_{2}}{u_{1}}=\frac{u_{3}}{u_{2}}

∴ r=\frac{1+2d}{1+d}=\frac{1+5d}{1+2d}

- Use cross multiplication with the equal fractions

∵ \frac{1+2d}{1+d}=\frac{1+5d}{1+2d}

∴ (1 + 2d)(1 + 2d) = (1 + d)(1 + 5d)

∴ 1 + 2d + 2d + 4d² = 1 + 5d + d + 5d²

- Add like terms in each side

∴ 1 + 4d + 4d² = 1 + 6d + 5d²

- Subtract 1 from both sides

∴ 4d + 4d² = 6d + 5d²

- Subtract 4d from both sides

∴ 4d² = 2d + 5d²

- Subtract 4d² from each side

∴ 0 = 2d + d²

- Take d as a common factor

∴ 0 = d(2 + d)

- Equate each factor by 0

∴ d = 0 but we will reject it because d ≠ 0

∴ 2 + d = 0

- Subtract 2 from both sides

∴ d = -2

The value of d is -2

Learn more:

You can learn more about the sequence in brainly.com/question/1522572

#LearnwithBrainly

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