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Sequences and Series Test - 26

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Sequences and Series Test - 26
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  • Question 1
    1 / -0
    Find the value of $$'?'$$ in the series: $$12, 17, 15, ?, 18, 23, 21,....$$
    Solution
    The series alternates the addition of $$5$$ with the subtraction of $$2$$.
    So, the number is $$20$$.
  • Question 2
    1 / -0
    Choose the missing number in the series: $$2, 2, 3, 4, 4,$$__$$, 6, 6, 7, 8, 8, 9....$$
    Solution
    This is a continuous series of adding $$1$$ to the previous number, in which every third number is not repeated.
    So, the missing number is $$5$$.
  • Question 3
    1 / -0
    Find the value of $$'x'$$ in the series: $$144, 169, x, 225, 256, 289$$.
    Solution
    The series is a perfect square in increasing order of $$12, 13, 14, 15...$$
    So, the value of $$x$$ is $$196$$.
  • Question 4
    1 / -0
    The value of $$\displaystyle \tan { \alpha  } +2\tan { \left( 2\alpha  \right)  } +4\tan { \left( 4\alpha  \right)  } +...+{ 2 }^{ n-1 }\tan { \left( { 2 }^{ n-1 }\alpha  \right)  } +{ 2 }^{ n }\cot { \left( { 2 }^{ n }\alpha  \right)  } $$ is
    Solution
    Now, $$\displaystyle { 2 }^{ n }\tan { \left( { 2 }^{ n }a \right)  } +{ 2 }^{ n }\cot { \left( { 2 }^{ n }a \right)  } $$
    $$\displaystyle ={ 2 }^{ n-1 }\left[ \frac { \sin { { 2 }^{ n-1 }a }  }{ \cos { { 2 }^{ n-1 }a }  } +2\frac { \cos { { 2 }^{ n }a }  }{ \sin { { 2 }^{ n }a }  }  \right] $$
    $$\displaystyle ={ 2 }^{ n-1 }\left[ \frac { \cos { { 2 }^{ n }a } \cos { { 2 }^{ n-1 }a } +\sin { { 2 }^{ n }a\sin { { 2 }^{ n-1 }a+\cos { { 2 }^{ n }a } \cos { { 2 }^{ n-1 }a }  }  }  }{ \sin { { 2 }^{ n }a\cos { { 2 }^{ n-1 }a }  }  }  \right] $$
    $$\displaystyle ={ 2 }^{ n-1 }\left[ \frac { \cos { { 2 }^{ n-1 }a } \left( 1+\cos { { 2 }^{ n }a }  \right)  }{ \sin { { 2 }^{ n }a } \cos { { 2 }^{ n-1 }a }  }  \right] $$
    $$\displaystyle ={ 2 }^{ n-1 }\cot { { 2 }^{ n-1 }a } $$
    Proceeding in similar way in last, we get
    $$\displaystyle \tan { a } +2\cot { 2a } $$
    $$\displaystyle =\frac { \sin { a }  }{ \cos { a }  } +2\frac { \cos { 2a }  }{ \sin { 2a }  } $$
    $$\displaystyle =\frac { \cos { 2a\cos { a } +\sin { 2a } \sin { a } +\cos { 2a\cos { a }  }  }  }{ \sin { 2a\cos { a }  }  } $$
    $$\displaystyle =\frac { \cos { a } \left( 1+\cos { 2a }  \right)  }{ 2\sin { a } { cos }^{ 2 }a } =\frac { 2{ cos }^{ 2 }a }{ 2\sin { a }  } $$
    $$\displaystyle =\frac { \cos { a }  }{ \sin { a }  } =\cot { a } $$
  • Question 5
    1 / -0
    Find the missing number in the pattern: $$2, 5, 8, 11,$$ __$$, 17, 20, 23, 26$$
    Solution
    The series adds $$3$$ to each number to get the next number.
    So, the next number is $$11 + 3 = 14$$
  • Question 6
    1 / -0
    Which number comes next?
    $$5, 9, 13, 17, 21, 25, 29,...$$
    Solution
    The series adds $$4$$ to each number to get the next number.
    So, the next number is $$29 + 4 = 33$$
  • Question 7
    1 / -0
    The sum of $$24$$ terms of the following series $$2+4+6.....$$
    Solution
    $$\overline { 2 } +\overline { 8 } +\overline { 18 } +\overline { 32 } ......24$$terms
    $$=\sqrt { 2 } +\sqrt { 8 } +\sqrt { 18 } +\sqrt { 32 } .....24$$terms
    $$\\ =\sqrt { 2 } (1+\sqrt { 4 } +\sqrt { 9 } +\sqrt { 16 } +........24$$terms)
    $$ =\sqrt { 2 } (1+2+3+4+.....24)$$
    Sum of natural number$$=\cfrac { n(n+1) }{ 2 } $$
    $$ =\sqrt { 2 } \cfrac { (24)(25) }{ 2 } \\ =300\sqrt { 2 } =300\overline { 2 } $$
    Answer$$(C)$$
  • Question 8
    1 / -0
    $$2, 3,$$ __$$, 4, 4, 5, 6, 6, 6, 7, 7, 7...$$ What number should fill the blank?
    Solution

  • Question 9
    1 / -0
    Fill in the blank: $$62, 66, 63, 66, 64,$$ __$$, 65,....$$
    Solution
    The series alternates the addition of $$4$$ with the subtraction of $$3$$.
    So, the missing number is $$61$$.
  • Question 10
    1 / -0
    Identify the missing integer: $$9, 45,$$ ____$$, 1125, 5625...$$
    Solution
    This is continuous series multiplied by $$5$$.
    $$9 \times  5 = 45$$
    $$45 \times  5 = 225$$
    $$225 \times  5 = 1,125$$
    $$1,125 \times  5= 5,625.$$
    So, the missing integer is $$225$$.
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