GRE Subject Test: Math : Calculus

Study concepts, example questions & explanations for GRE Subject Test: Math

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Example Questions

Example Question #4 : Sequences & Series

If a sequence is 9, 3, -3, -9, -15, ...

What is the 10th term of the sequence?

Possible Answers:

\displaystyle -45

\displaystyle -6

\displaystyle -39

\displaystyle -27

\displaystyle -81

Correct answer:

\displaystyle -45

Explanation:

It will be helpful if you can see that the sequence is changing by -6 to get to each number. The quickest way to solve this is to keep going with the sequence by subtracting six from each number to get to the next number.

9, 3, -3, -9, -15, -21, -27, -33, -39, -45

-45 is the 10th number in the sequence.

Another way to find the 10th term is by using the equation for arithmetic sequences.

\displaystyle a_n=a_1+(n-1)d

where \displaystyle a_n is the term in question, \displaystyle a_1 is the first term, \displaystyle n is the numbered term, and \displaystyle d is the difference of the terms.

To find d subtract the first two terms.

\displaystyle 3-9=-6

Therefore, the equation becomes

\displaystyle a_{10}=9+(10-1)(-6)

\displaystyle \\a_{10}=9+(9)(-6)\\a_{10}=9-54\\a_{10}=-45

 

Example Question #11 : Sequences & Series

The first 3 terms of a geometric sequence are 5,9, and 13. What is the 15th term?

Possible Answers:

\displaystyle 63

\displaystyle 59

\displaystyle 61

\displaystyle 57

Correct answer:

\displaystyle 61

Explanation:

Step 1: We know it's a geometric sequence, so the difference between each consecutive term is the same. We must find the difference.

\displaystyle Difference=9-5=4

Step 2: For every term after the first term, we will add a multiple of \displaystyle 4n to the first term. 

Step 3: We can write an equation that helps us find the nth term of the sequence. We add a multiple of 4n to 5; the equation becomes \displaystyle 4n+5.

Step 4: We need to find the value of n. We want the 15th number and we are given the first number. There are \displaystyle 14 numbers in between, so n=14.

Step 5: Plug in 14 for n and find the 15th term

\displaystyle 15th\ Term=5+4(14)=5+56=61

The \displaystyle 15th term is \displaystyle 61

Example Question #1 : Finding Terms Of A Sequence

The first three terms of a arithmetic sequence are \displaystyle 4,9, 14. What is the \displaystyle 15th term of this sequence?

Possible Answers:

\displaystyle 77

\displaystyle 62

\displaystyle 74

\displaystyle 63

Correct answer:

\displaystyle 74

Explanation:

Step 1: We need to find the difference between the terms. To find the difference, subtract the first two terms.

Difference=\displaystyle 9-4=5

Step 2: To find the next term of a arithmetic sequence, we add the difference to the previous term.

Fourth term=\displaystyle 3rd term+5
\displaystyle 4th term=\displaystyle 14+5=19. The fourth term is 19.

Step 3: To find the \displaystyle nth term, we must add a multiple of \displaystyle 5n to the first term. In this problem, we are given the \displaystyle 1st term, so we need to find how many terms are in between the \displaystyle 15th and \displaystyle 1st term.

\displaystyle 15-1=14. This tells me that I have to add \displaystyle 5 fourteen times to get to the \displaystyle 15th term. \displaystyle n=14.

Step 4: Now that we know what the value of n, we can plug it in to the equation:

\displaystyle 4+5n, where 4 is the starting number, and n represents how many times I need to add 5 to the next term (and up to the 15th term).

Let's plug it in:

\displaystyle 4+5(14)=4+70=74.

So, the \displaystyle 15th term in this sequence is \displaystyle 74.

Example Question #1 : Finding Terms Of A Sequence

What is the next number in the sequence: \displaystyle 196,144,100,64,?

Possible Answers:

\displaystyle 25

\displaystyle 36

\displaystyle 49

\displaystyle 256

Correct answer:

\displaystyle 36

Explanation:

Step 1: Try to find a pattern in the sequence

\displaystyle 196=14^2
\displaystyle 144=12^2

\displaystyle 100=10^2
\displaystyle 64=8^2

The pattern is decreasing perfect squares, the difference between each base of the consecutive term is \displaystyle 2..

Step 2: Find the next term...

If the base of the next term goes down by \displaystyle 2, the next term is \displaystyle 6^2..

\displaystyle 6^2=36

The next term of this sequence is \displaystyle 36.

Example Question #171 : Calculus

What is the next term in the sequence: \displaystyle 0,3,8,15,24,?

Possible Answers:

\displaystyle 80

\displaystyle 63

\displaystyle 35

\displaystyle 48

Correct answer:

\displaystyle 35

Explanation:

Step 1: Try to find the difference between the terms.

Difference between \displaystyle 0 and \displaystyle 3 is \displaystyle 3.
Difference between \displaystyle 3 and \displaystyle 8 is \displaystyle 5.
Difference between \displaystyle 8 and \displaystyle 15 is \displaystyle 7.

Difference between \displaystyle 15 and \displaystyle 24 is \displaystyle 9.

The difference between consecutive numbers is an odd number, and the difference between the consecutive terms is always \displaystyle 2..

The difference between \displaystyle ? and \displaystyle 24 is \displaystyle 9+2=11

\displaystyle ?=24+11=35

The next number in the sequence is \displaystyle 35.

Example Question #5 : Finding Terms Of A Sequence

Find the next term in the sequence: \displaystyle 1,1,2,3,5,8,?

Possible Answers:

\displaystyle 8

\displaystyle 34

\displaystyle 13

\displaystyle 21

Correct answer:

\displaystyle 13

Explanation:

Step 1: Find the next term in the sequence: \displaystyle 1,1,2,3,5,8,?

Step 2: Can you recognize the sequence here??

This is the Fibonacci Sequence.. The sum of the previous two terms is equal to the next consecutive term..

\displaystyle 1+1=2
\displaystyle 1+2=3
\displaystyle 2+3=5
\displaystyle 3+5=8
\displaystyle 5+8=?, ?=13

The missing term is 13.

Example Question #11 : Sequences

What is the next term in the sequence: \displaystyle 3,9,15,21,27,...

Possible Answers:

\displaystyle 33

\displaystyle 35

\displaystyle 34

\displaystyle 37

Correct answer:

\displaystyle 33

Explanation:

Step 1: Find the difference between each two consecutive terms...

The difference is always 6 because we have a sequence...

Step 2: Find the next term in the sequence..

\displaystyle 27+6=33

The next term is \displaystyle 33.

Example Question #8 : Finding Terms Of A Sequence

Find the next term in the following sequence: \displaystyle 7,16,25,34,43,x

Possible Answers:

\displaystyle 47

\displaystyle 50

\displaystyle 52

\displaystyle 43

Correct answer:

\displaystyle 52

Explanation:

Step 1: Calculate the difference between the terms...

\displaystyle 7\rightarrow16, add 9
\displaystyle 16\rightarrow25, add 9
\displaystyle 25\rightarrow34, add 9

Step 2: We found the pattern between the terms..

So, we can add 9 to the term before the \displaystyle x to find the value of \displaystyle x..

\displaystyle 43+9=52

The missing term (the next term) in the sequence is \displaystyle 52.

Example Question #1 : Finding Terms Of A Sequence

If the first term of an arithmetic sequence is 2 and the third term is 8, find the \displaystyle \large \large 16th term.

Possible Answers:

\displaystyle \large 47

\displaystyle \large 46

\displaystyle \large 43

\displaystyle \large 49

Correct answer:

\displaystyle \large 47

Explanation:

Step 1: Find the difference between each term...

Subtract the first term from the third term...

\displaystyle \large 8-2=6
There are two terms between first and third...Take the answer in step 1 and divide by 2 to get the difference between consecutive terms...

\displaystyle \large \frac {6}{2}=3

The common difference is \displaystyle \large 3.

Step 2: Find an equation that describes the sequence....

The equation is \displaystyle \large 3n+2, where \displaystyle \large n represents how many terms I need to calculate and \displaystyle \large 2 is the first term... 

Step 3: Plug in \displaystyle \large n...

To find n, we subtract the term that we want from the original term...

So, if we want the \displaystyle \large 16th term and we are given the first term...

Then \displaystyle \large n=16-1=15

So, \displaystyle \large 3(15)+2=45+2=47

The \displaystyle \large 16th term is \displaystyle \large 47.

Example Question #3 : Finding Terms Of A Sequence

If the first \displaystyle 4 terms of a sequence are \displaystyle 4,11,20,31,find the \displaystyle 32th term.

Possible Answers:

\displaystyle 2016

\displaystyle 1251.\overline {11}

\displaystyle 1151

\displaystyle 1250

Correct answer:

\displaystyle 1151

Explanation:

Step 1: Find the successive difference rows until we get equal values between every two consecutive numbers.

\displaystyle 4,11,20,31

\displaystyle 7,9,11

\displaystyle 2,2

Step 2: Since we obtain equal values for the successive differences in the second row, hence the \displaystyle n^{th} term of the sequence is a second-degree polynomial. 

So, the \displaystyle n^{th} term takes the form of

\displaystyle a_n=An^2+Bn+C

Step 3: Now, substituting \displaystyle n=1,2,3 into the formula, we get:

\displaystyle A+B+C=4...........(1)

\displaystyle 4A+2B+C=11........(2)

\displaystyle 9A+3B+C=20.........(3)

\displaystyle (2)-(1):3A+B=7.......(4)

\displaystyle (3)-(2):5A+B=9.......(5)

\displaystyle (5)-(4):2A=2

\displaystyle A=1

\displaystyle B=7-3(1)=4

\displaystyle C=4-4-1=-1

Step 4: Solve the system of linear equations:

\displaystyle A=1, B=4, C=-1

So, the  \displaystyle n^{th} term takes the form:

\displaystyle n^2+4n-1

Step 5: Plug in \displaystyle n=32 into the form...

\displaystyle (32)^2+4(32)-1

\displaystyle 1024+128-1

\displaystyle 1151

 

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