A sequence refers to a list of numbers with some inherent pattern.
General term of a sequence, generally written as an is an expression that for different values of ‘n’ gives different terms of the sequence.
A sequence of the type a,a+d,a+2d,a+3d,… is said to form an AP.
Each term differs from the previous one by a fixed value called as “common difference”.
a and d are usually used to denote first term and common difference respectively. nth term of an AP is given by
an=a1+(n-1)dThe tutorial will show you how to compute the sum of the first n terms of an AP
3 terms in an AP are – a-d,a,a+d
4 terms in an AP are – a-3d,a-d,a+d,a+3d
And so on.
mth term from the end of an AP : It is the (n-m+1)th term from the beginning.
Alternately, we can reverse the AP, and consider the first term and common difference of the new AP as last term and negative of common difference of the old AP.
If a constant is added, or subtracted, or multiplied or divided from every term on an AP, the resulting sequence is still an AP.
if a,b,c are in AP, then b is said to be arithmetic mean of a and c.
Equivalently, if 2b=a+c, then a,b,c are in AP. If between a and b we are to insert n numbers A1,A2,A3,….,An such that a, A1,A2,A3,….,An form an AP, then A1,A2,A3,….,An are called n Arithmetic Means.
A sequence of the type: a,ar,ar2,ar3,… is called a GP.
In a GP, the nth term of a GP is given by: an=arm-1
The tutorial will show you how to compute the sum of first n terms of a GP.
When r=1, the GP can be treated as an AP, and clearly the sum of first n terms then is “nXa”.
Similar to an AP, mth term from the end is (n-m+1)th term from the starting.
A GP of 3 terms : a/r,a,ar
A GP of 4 terms:a/r3,a/r,ar,ar3
And so on.
If all terms in a GP are multiplied or divided by the same number, or are raised to the same power, then the resulting sequence is still a GP.
If a,b,c are in GP then b2=ac and b is called the GM of a and c. Conversely, if b2=ac, then a,b,c are in GP.
Sum of infinite terms of a GP: If -1<r<1, then GP is said to converge, that is to say that sum of infinite terms of such a GP tends to a constant value.
If a sequence is in AP, then the sequence obtained by taking the reciprocal of every term in the sequence forms an HP.
That is if a,b,c,… form an AP, then 1/a,1/b,1/c,… form an HP.
Let a,b,c form an HP. Then clearly, 1/a,1/b,1/c form an AP.
b is called the Harmonic Mean.
Problems related to HP are generally solved by converting it into an AP.
NOTE: Let a,b be two positive real numbers. Then
AM X HM=GM2.
Q: What is the common difference of an AP whose nth term is xn+y?
Q: If the sum of n terms of an AP is 2n2+3n, what is the kth term?
Q: If am=n and an=m, what is ap?
Q: If the sums of n terms of two arithmetic progressions are in the ratio 2n+5:3n+4, then what is the
ratio of their nth terms?
Q: If sum of n terms of an AP is 3n2+5n then which of its terms is 164?
Q: If sum of first p terms is q and sum of first q terms is p then what is the sum of first p+q terms ?
Q: If four numbers are in AP such that their sum is 50, and the greatest number is four times the least,
then what are the numbers?
Q: If n arithmetic means are inserted between 1 and 31 such that ratio of first and nth mean is 3:29,
then what is the value of n?
Q: If S1 is the sum of an AP of ‘n’ odd number of terms and S2 the sum of terms of the series in odd
places, then what is S1/S2?
Q: What is the sum of 2 digit multiples of 4?
Q: Find the sum of 2+6+18+…+4374.
Q: Find the sum of 5+55+555+…n terms
Q: Find the sum of n terms of the sequence whose nth term is 2n+3n
Q: Find a GP for which the sum of first two terms is -4 and the fifth term is 4 times the third term.
Q: Find the least value of n for which the sum of 1+3+9+27+… to n terms is greater than 7000.
Q: If a,b,c are in GP, prove that log a, log b, log c are in AP and vice versa.
Q: If a,b,c are in GP and x,y are AM’s between a,b and b,c respectively, then prove that x,b,y are in HP.
Q: Find the sum to n terms of series 1.2.3+2.3.4+3.4.5+4.5.6+…
Q: If a, b, c are in H.P., show that a/b+c, b/c+a, c/a+b are also in H.P.
Q: Evaluate: 62 + 72 + 82 + 92 + 102
Q: Prove that (a + b + c) (ab + bc + ca) > 9abc.
Q: If a2, b2, c2 are in A.P. show that b+ c, c, c+ a, a + b are in H.P.
Q: If the AM between ‘a’ and ‘b’ is twice as greater as the GM, show that a/b = 7+4√3
Q: Sum to the n terms the series, 12-22+32-42+… n is even.
MCQ Quiz/Worksheet #3 : More on Geometric Progressions.
Answer Submission Form for MCQ Quiz #3
Answer Submission Form for MCQ Quiz #4
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