Sequences and Series

If $\theta_{1}, \theta_{2}, \theta_{3}, \ldots, \theta_{n}$ are in A.P., whose common difference is d, show that $\operatorname{Sec} \theta_{1} \sec \theta_{2}+\sec \theta_{2} \sec \theta_{3}+\ldots+\sec \theta_{n-1} \sec \theta_{n}=\frac{\tan \theta_{\mathrm{n}}-\tan \theta_{1}}{\operatorname{sind}}$

Solution: It is given that $\theta_{1}, \theta_{2}, \theta_{3}, \ldots, \theta_{n}$ are in the form of A.P., and $d$ is the common difference, We now need to prove that $\operatorname{Sec}...

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If the $\mathrm{p}^{\text {th }}$ and $\mathrm{q}^{\text {th }}$ terms of a G.P. are $q$ and $p$ respectively, show that its $(p+q)^{\text {th }}$ term is $\left(\frac{\mathrm{q}^{\mathrm{p}}}{\mathrm{p}^{q}}\right)^{\frac{1}{\mathrm{p}-\mathrm{q}}}$

Solution: The $n^{\text {th }}$ term of Geometric Progression is given by $t_{n}=a r^{n-1}$ in which the first term is $a$ and the common difference is $r$ $\mathrm{p}^{\text {th }}$ term is given...

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The first term of an A.P.is a, and the sum of the first $p$ terms is zero, show that the sum of its next q terms is $\frac{\text { is }(p+q) q}{p-1}$. [Hint: Required sum $\left.=\mathrm{S}_{\mathrm{p}+\mathrm{q}}-\mathrm{S}_{\mathrm{p}}\right]$

Solution: It is given that the first term is ' $a$ ' and the sum of first '$p$' terms is $S_{p}=0$ We now need to find the sum of the next 'q' terms So, the total terms are $p+q$ As a result, Sum of...

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In a cricket tournament 16 school teams participated. A sum of Rs 8000 is to be awarded among themselves as prize money. If the last placed team is awarded Rs 275 in prize money and the award increases by the same amount for successive finishing places, how much amount will the first place team receive?

Solution: Let the sum got by the lead position group be a Rs and d be distinction in sum As the thing that matters is same subsequently the runner up will get a – d and the third spot a – 2d, etc...

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In a potato race 20 potatoes are placed in a line at intervals of 4 metres with the first potato 24 metres from the starting point. A contestant is required to bring the potatoes back to the starting place one at a time. How far would he run in bringing back all the potatoes?

Solution: Given at start he needs to run 24m to get the main potato then 28 m as the following potato is 4m away from first, and so on Thus the succession of his running will be 24, 28, 32 … There...

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A side of an equilateral triangle is 20cm long. A second equilateral triangle is inscribed in it by joining the mid points of the sides of the first triangle. The process is continued as shown in the accompanying diagram. Find the perimeter of the sixth inscribed equilateral triangle.

Solution: Say ABC is a triangle with $AB\text{ }=\text{ }BC\text{ }=\text{ }AC\text{ }=\text{ }20$ cm Let’s say that D, E and F are respectively the midpoints of AC, CB and AB  that are joined to...

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We know the sum of the interior angles of a triangle is 180°. Show that the sums of the interior angles of polygons with 3, 4, 5, 6, … sides form an arithmetic progression. Find the sum of the interior angles for a 21-sided polygon.

Solution: It is given that the sum of interior angles of a polygon having ‘n’ sides is denoted by $(n-2)\times {{180}^{\circ }}$ The sum of angles having 3 sides i.e n $=\text{ }3\text{ }is\text{...

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A man accepts a position with an initial salary of Rs 5200 per month. It is understood that he will receive an automatic increase of Rs 320 in the very next month and each month thereafter. (a) Find his salary for the tenth month (b) What is his total earnings during the first year?

Solution: It is given to us that in first month the man’s salary is Rs.5200 and then it increases by Rs.320 every month Therefore, 5200, 5200 + 320, 5200 + 640… will be the sequence so formed of his...

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150 workers were engaged to finish a job in a certain number of days. 4 workers dropped out on second day, 4 more workers dropped out on third day and so on. It took 8 more days to finish the work. Find the number of days in which the work was completed

How about we expect x to be the quantity of days in which 150 laborers finish the work.   Then, at that point, from the inquiry, we have   \[\mathbf{150x}\text{ }=\text{ }\mathbf{150}\text{ }+\text{...

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A person writes a letter to four of his friends. He asks each one of them to copy the letter and mail to four different persons with instruction that they move the chain similarly. Assuming that the chain is not broken and that it costs 50 paise to mail one letter. Find the amount spent on the postage when 8th set of letter is mailed.

It's seen that,  The quantities of letters sent structures a \[\mathbf{G}.\mathbf{P}.:\text{ }\mathbf{4},\text{ }\mathbf{42},\text{ }\ldots \text{ }\mathbf{48}\] Here, \[\mathbf{initial}\text{...

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The Fibonacci sequence is defined by \[\mathbf{1}\text{ }=\text{ }{{\mathbf{a}}_{\mathbf{1}}}~=\text{ }{{\mathbf{a}}_{\mathbf{2}}}~\mathbf{and}\text{ }{{\mathbf{a}}_{\mathbf{n}}}~=\text{ }{{\mathbf{a}}_{\mathbf{n}\text{ }\text{ }\mathbf{1}~}}+\text{ }{{\mathbf{a}}_{\mathbf{n}\text{ }\text{ }\mathbf{2}}},\text{ }\mathbf{n}\text{ }>\text{ }\mathbf{2}\]. Find \[{{\mathbf{a}}_{\mathbf{n}+\mathbf{1}}}/{{\mathbf{a}}_{\mathbf{n}}},\text{ }\mathbf{for}\text{ }\mathbf{n}\text{ }=\text{ }\mathbf{1},\text{ }\mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{4},\text{ }\mathbf{5}~\]

Given, \[\begin{array}{*{35}{l}} 1\text{ }=\text{ }{{a}_{1}}~=\text{ }{{a}_{2}}  \\ {{a}_{n}}~=\text{ }{{a}_{n\text{ }\text{ }1~}}+\text{ }{{a}_{n\text{ }\text{ }2}},\text{ }n\text{ }>\text{ }2 ...

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Write the first five terms of each of the sequences and obtain the corresponding series: \[~{{\mathbf{a}}_{\mathbf{1}}}~=\text{ }{{\mathbf{a}}_{\mathbf{2}~}}=\text{ }\mathbf{2},\text{ }{{\mathbf{a}}_{\mathbf{n}}}~=\text{ }{{\mathbf{a}}_{\mathbf{n}-\mathbf{1}}}~\text{ }\mathbf{1},\text{ }\mathbf{n}\text{ }>\text{ }\mathbf{2}\]

Given, \[{{a}_{1}}~=\text{ }{{a}_{2}},\text{ }{{a}_{n}}~=\text{ }{{a}_{n-1}}~\text{ }1\] Then, at that point, \[\begin{array}{*{35}{l}} {{a}_{3}}~=\text{ }{{a}_{2}}~\text{ }1\text{ }=\text{ }2\text{...

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Write the first five terms of each of the sequences and obtain the corresponding series: \[~{{\mathbf{a}}_{\mathbf{1}}}~=\text{ }-\mathbf{1},\text{ }{{\mathbf{a}}_{\mathbf{n}}}~=\text{ }{{\mathbf{a}}_{\mathbf{n}-\mathbf{1}}}/\mathbf{n},\text{ }\mathbf{n}\text{ }\ge \text{ }\mathbf{2}\]

Given, \[{{a}_{n}}~=\text{ }{{a}_{n-1}}/n\text{ }and\text{ }{{a}_{1}}~=\text{ }-1\] Then, at that point, \[\begin{array}{*{35}{l}} {{a}_{2}}~=\text{ }{{a}_{1}}/2\text{ }=\text{ }-1/2  \\...

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Write the first five terms of each of the sequences and obtain the corresponding series: \[~{{\mathbf{a}}_{\mathbf{1}}}~=\text{ }\mathbf{3},\text{ }{{\mathbf{a}}_{\mathbf{n}}}~=\text{ }\mathbf{3}{{\mathbf{a}}_{\mathbf{n}-\mathbf{1}}}~+\text{ }\mathbf{2}\text{ }\mathbf{for}\text{ }\mathbf{all}\text{ }\mathbf{n}\text{ }>\text{ }\mathbf{1}\]

Given, \[{{a}_{n}}~=\text{ }3{{a}_{n-1}}~+\text{ }2\text{ }and\text{ }{{a}_{1}}~=\text{ }3\] Then, at that point, \[\begin{array}{*{35}{l}} {{a}_{2}}~=\text{ }3{{a}_{1}}~+\text{ }2\text{ }=\text{...

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