Definite integrals and the fundamental theorem of calculus.

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More Challenging Problems

 

1. Using only geometry, find the integral of y = 1 – x from x = 0 to x = 1.

   

Answer

1. 1/2

 Solution

1. The function y = 1 – x is a straight line. Its value is 1 at x = 0, and 0 at x = 1. Under it is the right triangle with vertices (0,0), (0,1), (1,0). It covers half of the unit square, and its area is 1/2.

 

2. Find ∫ x2 dx from 0 to 1

Answer

    1. 1/3

Solution

1. We need the anti-derivative of x2. Our table of anti-derivatives says that we can use F(x) = x3/3. The value of the integral is: F(1) – F(0) = 1/3 – 0/3 = 1/3.

 

3. Find ∫ 1/x dx from 1 to 10.

     

Answer

1. ln(10)

 Solution

1. Using the table of common integrals says that we can use F(x) = ln(x) as anti-derivative. The integral is F(10) – F(1) = ln(10) – ln(1), = ln(10), (since ln(1) = 0).

 

4. Find ∫ sin(x) dx from 0 to π.

Answer

1. 2

 Solution

1. Our table of anti-derivatives says that we can take F(x) = -cos(x). The value of the integral is: F(π) – F(0) = -cos(π) – [-cos(0)], = -(-1) + 1 = 2

 

5. Find ∫e3x dx from -1 to 1.

   

Answer

1. [e3 – e-3] / 3

Solution

    1. The derivative of e3x is 3e3x. To get e3x, we can take F(x) = e3x/3. The value of our integral is F(1) – F(-1) = e3/3 – e-3/3 = [e3 – e-3] /3.