GRE Subject Test: Math : Numerical Integration

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

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Example Questions

Example Question #11 : How To Find Midpoint Riemann Sums

Solve the integral

\(\displaystyle \int_{1}^{5}{\frac{1}{x-7}}dx\)

using Simpson's rule with \(\displaystyle 2n=10\) subintervals.  

Possible Answers:

\(\displaystyle -0.500\)

\(\displaystyle -0.1667\)

\(\displaystyle -1.0987\)

\(\displaystyle -1.6667\)

\(\displaystyle -8.2400\)

Correct answer:

\(\displaystyle -1.0987\)

Explanation:

Simpson's rule is solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx =S_{2m}=\frac{1}{3}(\frac{b-a}{2n})\left [ f(0)+4f(1)+2f(2)+...+2f(m-2)+4f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{5-1}{10})=0.4\).  

The value of each approximation term is below.

Screen shot 2015 06 11 at 9.35.50 pm 

The sum of all the approximation terms is \(\displaystyle -8.23995\) therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.4)*(-8.23995)=-1.0987\)

Example Question #2 : Numerical Integration

Solve the integral

\(\displaystyle \int_{8}^{15}{ln(x)}dx\)

using Simpson's rule with \(\displaystyle 2n=10\) subintervals.  

Possible Answers:

\(\displaystyle 8.6532\)

\(\displaystyle 2.0794\)

\(\displaystyle 10.2289\)

\(\displaystyle 10.6410\)

\(\displaystyle 16.9852\)

Correct answer:

\(\displaystyle 16.9852\)

Explanation:

Simpson's rule is solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx=S_{2m}=\frac{1}{3}(\frac{b-a}{2n})\left [ f(0)+4f(1)+2f(2)+...+2f(m-2)+4f(m-1)+f(m) \right ]\)

where \(\displaystyle 2n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{15-8}{10})=0.7\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 9.35.58 pm

The sum of all the approximation terms is \(\displaystyle 72.79378\) therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.7)*(72.79378)=16.9852\)

Example Question #12 : How To Find Midpoint Riemann Sums

Solve the integral

\(\displaystyle \int_{-1}^{1}{\frac{1}{2+cos(x)}}dx\)

using Simpson's rule with \(\displaystyle 2n=10\) subintervals.  

Possible Answers:

\(\displaystyle 1.2340\)

\(\displaystyle 10.5872\)

\(\displaystyle 10.9830\)

\(\displaystyle 0.7056\)

\(\displaystyle 0.3948\)

Correct answer:

\(\displaystyle 0.7056\)

Explanation:

Simpson's rule is solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx =S_{2m}=\frac{1}{3}(\frac{b-a}{2n})\left [ f(0)+4f(1)+2f(2)+...+2f(m-2)+4f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{1+1}{10})=0.2\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 9.36.10 pm

The sum of all the approximation terms is \(\displaystyle 10.5840\) therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.2)*(10.5840)=0.7056\)

Example Question #1 : Simpson's Rule

Solve the integral

\(\displaystyle \int_{0}^{9}{\frac{1}{1+e^{x}}}dx\)

using Simpson's rule with \(\displaystyle 2n=10\) subintervals.  

Possible Answers:

\(\displaystyle 0.6924\)

\(\displaystyle 0.6599\)

\(\displaystyle 1.2369\)

\(\displaystyle 0.8829\)

\(\displaystyle 0.3482\)

Correct answer:

\(\displaystyle 0.6924\)

Explanation:

Simpson's rule is solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx\approx S_{2m}=\frac{1}{3}(\frac{b-a}{2n})\left [ f(0)+4f(1)+2f(2)+...+2f(m-2)+4f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{9-0}{10})=0.9\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 9.36.20 pm

The sum of all the approximation terms is \(\displaystyle 2.3081\) therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.9)*(2.3081)=0.6924\)

Example Question #1 : Trapezoidal Rule

Solve the integral

\(\displaystyle \int_{2}^{7}{\frac{1}{5x+3}}dx\)

using the trapezoidal approximation with \(\displaystyle n=5\) subintervals.  

Possible Answers:

\(\displaystyle 0.8603\)

\(\displaystyle 0.4301\)

\(\displaystyle 0.7601\)

\(\displaystyle 0.5233\)

\(\displaystyle 0.9548\)

Correct answer:

\(\displaystyle 0.4301\)

Explanation:

 Trapezoidal approximations are solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx\approx T_{n}=(\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{7-2}{2*5})=0.5\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 8.19.15 pm

The sum of all the approximation terms is \(\displaystyle 0.86027754\), therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.5)*(0.86027754)=0.4301\)

Example Question #2 : Trapezoidal Rule

Solve the integral

\(\displaystyle \int_{1}^{2}{x\sin (x)}dx\)

using the trapezoidal approximation with \(\displaystyle n=5\) subintervals.  

Possible Answers:

\(\displaystyle 28.7867\)

\(\displaystyle 0.8415\)

\(\displaystyle 2.8787\)

\(\displaystyle 2.5052\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 2.8787\)

Explanation:

 Trapezoidal approximations are solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx\approx T_{n}=(\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{2-1}{2*5})=0.1\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 8.32.39 pm

The sum of all the approximation terms is \(\displaystyle 28.7867\), therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.1)*(28.786699)=2.8787\)

Example Question #7 : Numerical Integration

Solve the integral

\(\displaystyle \int_{0}^{4}{\sqrt{5+x^{^{3}}}}dx\)

using the trapezoidal approximation with \(\displaystyle n=5\) subintervals.  

Possible Answers:

\(\displaystyle 33.5582\)

\(\displaystyle 14.3744\)

\(\displaystyle 5.0000\)

\(\displaystyle 2.3547\)

\(\displaystyle 83.8900\)

Correct answer:

\(\displaystyle 33.5582\)

Explanation:

 Trapezoidal approximations are solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx\approx =T_{n}=(\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{4-0}{2*5})=0.4\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 8.55.34 pm

The sum of all the approximation terms is \(\displaystyle 83.89553\), therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.4)*(83.89553)=33.5582\)

Example Question #2 : Trapezoidal Rule

Solve the integral

\(\displaystyle \int_{1}^{2}{\sqrt{ln(x)}}dx\)

using the trapezoidal approximation with \(\displaystyle n=5\) subintervals.  

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 0.6174\)

\(\displaystyle 11.7257\)

\(\displaystyle 0.8326\)

\(\displaystyle 1.1726\)

Correct answer:

\(\displaystyle 1.1726\)

Explanation:

 Trapezoidal approximations are solved using the formula

\(\displaystyle \int_{a}^{b}f(x))dx\approx T_{n}=(\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]\)

where \(\displaystyle n\) is the number of subintervals and \(\displaystyle f(m)\) is the function evaluated at the midpoint.

For this problem, \(\displaystyle (\frac{b-a}{2n})=(\frac{2-1}{2*5})=0.1\).  

The value of each approximation term is below.

 Screen shot 2015 06 11 at 8.55.45 pm

The sum of all the approximation terms is \(\displaystyle 11.7257431\), therefore

\(\displaystyle (\frac{b-a}{2n})\left [ f(0)+2f(1)+...+f(m-1)+f(m) \right ]=(0.1)*(11.7257431)=1.1726\)

Example Question #9 : Numerical Integration

Evaluate  \(\displaystyle \int_{0}^{2} x^{x^{2}} dx\) using the Trapezoidal Rule, with n = 2.

Possible Answers:

\(\displaystyle 2.0\)

\(\displaystyle 16.0\)

\(\displaystyle 9.0\)

\(\displaystyle 8.5\)

\(\displaystyle 5.0\)

Correct answer:

\(\displaystyle 9.0\)

Explanation:

1) n = 2 indicates 2 equal subdivisions. In this case, they are from 0 to 1, and from 1 to 2.

2) Trapezoidal Rule is: \(\displaystyle \int_{a}^{b} f(x)dx \approx \left [ b-a\right ]\left [ \frac{f(a)+f(b)}{2}\right ]\)

3) For n = 2: \(\displaystyle \int_{0}^2 x^{x^{2}} dx \approx [1-0]\left [ \frac{f(0)+f(1)}{2} \right ]+ [2-1]\left [ \frac{f(1)+f(2)}{2} \right ]\)

4) Simplifying: \(\displaystyle \int_{0}^2 x^{x^{2}} dx \approx [1]\left [ \frac{0+1}{2} \right ]+ [1]\left [ \frac{1+16}{2} \right ] = \frac{1}{2}+\frac{17}{2} = \frac{18}{2} = 9.\)

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