Sequences and Series
- Given that 1² + 2² + 3² + ... + 20² = 2870, the value of (2² + 4² + 6² + ..... + 40²) is :
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From the question ,
2² + 4² + 6² + .... + 40² = 2² (1² + 2² + 3² +.... + 20²)Correct Option: A
From the question ,
2² + 4² + 6² + .... + 40² = 2² (1² + 2² + 3² +.... + 20²)
Required answer = 4 × 2870 = 11480
- Given 1³ + 2³ + 3³ + ... + 10³ = 3025 then 2³ + 4³ + 6³ + ...+ 20³ is equal to
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It is given, 1³ + 2³ + 3³ + ... + 10³ = 3025 ........( 1 )
Now, 2³ + 4³ + 6³ + ... + 20³ = (1 × 2)³ + (2 × 2)³ + (2 × 3)³ + ... + (2 × 10)³
2³ + 4³ + 6³ + ... + 20³ = 2³ [1³ + 2³ + 3³ + ... + 10³]Correct Option: D
It is given, 1³ + 2³ + 3³ + ... + 10³ = 3025 ........( 1 )
Now, 2³ + 4³ + 6³ + ... + 20³ = (1 × 2)³ + (2 × 2)³ + (2 × 3)³ + ... + (2 × 10)³
2³ + 4³ + 6³ + ... + 20³ = 2³ [1³ + 2³ + 3³ + ... + 10³]
Using the value of equation ( 1 ) , we get
∴ 2³ + 4³ + 6³ + ... + 20³ = 8 × 3025 = 24200
- 4, 2, 3.5, 7.5, 26.25, 118.125
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Series pattern 4 x 0.5 = 2
2 x 1.5 = 3
Should come in place of 3.5
3 x 2.5 = 7.5Correct Option: C
Series pattern 4 x 0.5 = 2
2 x 1.5 = 3
Should come in place of 3.5
3 x 2.5 = 7.5
7.5 x 3.5 = 26.25
26.25 x 4.5 = 118.125
Clearly, 3.5 is wrong and is replaced by 3.
- If p, q, r, s are in harmonic progression and p > s, then —
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According to question,
If p, q, r, s are in HP.⇒ 1 , 1 , 1 , 1 are in AP. p q r s ⇒ 1 - 1 = 1 - 1 q p s r
Correct Option: D
According to question,
If p, q, r, s are in HP.⇒ 1 , 1 , 1 , 1 are in AP. p q r s ⇒ 1 - 1 = 1 - 1 q p s r ⇒ 1 + 1 = 1 + 1 q r s p
Hence, the none of these be answer
- What is the eighth term of the sequence 1, 4, 9, 16, 25 ..... ?
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According to question,
1 = (1)²
4 = (2)²
9 = (3)²
16 = (4)²
25 = (5)²
Each term of the progression is the square of a natural number.Correct Option: B
According to question,
1 = (1)²
4 = (2)²
9 = (3)²
16 = (4)²
25 = (5)²
Each term of the progression is the square of a natural number. Hence, the eighth term of the sequence will be (8)² = 64