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Key equations

To integrate products involving sin ( a x ) , sin ( b x ) , cos ( a x ) , and cos ( b x ) , use the substitutions.

  • Sine Products
    sin ( a x ) sin ( b x ) = 1 2 cos ( ( a b ) x ) 1 2 cos ( ( a + b ) x )
  • Sine and Cosine Products
    sin ( a x ) cos ( b x ) = 1 2 sin ( ( a b ) x ) + 1 2 sin ( ( a + b ) x )
  • Cosine Products
    cos ( a x ) cos ( b x ) = 1 2 cos ( ( a b ) x ) + 1 2 cos ( ( a + b ) x )
  • Power Reduction Formula
    sec n x d x = 1 n 1 sec n 1 x + n 2 n 1 sec n 2 x d x
  • Power Reduction Formula
    tan n x d x = 1 n 1 tan n 1 x tan n 2 x d x

Fill in the blank to make a true statement.

sin 2 x + _______ = 1

cos 2 x

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Use an identity to reduce the power of the trigonometric function to a trigonometric function raised to the first power.

sin 2 x = _______

1 cos ( 2 x ) 2

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Evaluate each of the following integrals by u -substitution.

sin 3 x cos x d x

sin 4 x 4 + C

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tan 5 ( 2 x ) sec 2 ( 2 x ) d x

1 12 tan 6 ( 2 x ) + C

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sin 7 ( 2 x ) cos ( 2 x ) d x

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tan ( x 2 ) sec 2 ( x 2 ) d x

sec 2 ( x 2 ) + C

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Compute the following integrals using the guidelines for integrating powers of trigonometric functions. Use a CAS to check the solutions. ( Note : Some of the problems may be done using techniques of integration learned previously.)

sin 3 x d x

3 cos x 4 + 1 12 cos ( 3 x ) + C = cos x + cos 3 x 3 + C

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sin x cos x d x

1 2 cos 2 x + C

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sin 5 x cos 2 x d x

5 cos x 64 1 192 cos ( 3 x ) + 3 320 cos ( 5 x ) 1 448 cos ( 7 x ) + C

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sin x cos x d x

2 3 ( sin x ) 2 / 3 + C

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sec x tan x d x

sec x + C

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tan 2 x sec x d x

1 2 sec x tan x 1 2 ln ( sec x + tan x ) + C

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sec 4 x d x

2 tan x 3 + 1 3 sec ( x ) 2 tan x = tan x + tan 3 x 3 + C

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csc x d x

ln | cot x + csc x | + C

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For the following exercises, find a general formula for the integrals.

sin 2 a x cos a x d x

sin 3 ( a x ) 3 a + C

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sin a x cos a x d x .

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Use the double-angle formulas to evaluate the following integrals.

0 π sin 2 x d x

π 2

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cos 2 3 x d x

x 2 + 1 12 sin ( 6 x ) + C

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sin 2 x d x + cos 2 x d x

x + C

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sin 2 x cos 2 ( 2 x ) d x

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For the following exercises, evaluate the definite integrals. Express answers in exact form whenever possible.

0 2 π cos x sin 2 x d x

0

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0 π sin 3 x sin 5 x d x

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0 π cos ( 99 x ) sin ( 101 x ) d x

0

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π π cos 2 ( 3 x ) d x

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0 2 π sin x sin ( 2 x ) sin ( 3 x ) d x

0

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0 4 π cos ( x / 2 ) sin ( x / 2 ) d x

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π / 6 π / 3 cos 3 x sin x d x (Round this answer to three decimal places.)

Approximately 0.239

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π / 3 π / 3 sec 2 x 1 d x

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0 π / 2 1 cos ( 2 x ) d x

2

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Find the area of the region bounded by the graphs of the equations y = sin x , y = sin 3 x , x = 0 , and x = π 2 .

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Find the area of the region bounded by the graphs of the equations y = cos 2 x , y = sin 2 x , x = π 4 , and x = π 4 .

1.0

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A particle moves in a straight line with the velocity function v ( t ) = sin ( ω t ) cos 2 ( ω t ) . Find its position function x = f ( t ) if f ( 0 ) = 0 .

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Find the average value of the function f ( x ) = sin 2 x cos 3 x over the interval [ π , π ] .

0

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For the following exercises, solve the differential equations.

d y d x = sin 2 x . The curve passes through point ( 0 , 0 ) .

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d y d θ = sin 4 ( π θ )

3 θ 8 1 4 π sin ( 2 π θ ) + 1 32 π sin ( 4 π θ ) + C = f ( x )

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Find the length of the curve y = ln ( csc x ) , π 4 x π 2 .

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Find the length of the curve y = ln ( sin x ) , π 3 x π 2 .

ln ( 3 )

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Find the volume generated by revolving the curve y = cos ( 3 x ) about the x -axis, 0 x π 36 .

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For the following exercises, use this information: The inner product of two functions f and g over [ a , b ] is defined by f ( x ) · g ( x ) = f , g = a b f · g d x . Two distinct functions f and g are said to be orthogonal if f , g = 0 .

Show that { sin ( 2 x ) , cos ( 3 x ) } are orthogonal over the interval [ π , π ] .

π π sin ( 2 x ) cos ( 3 x ) d x = 0

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Evaluate π π sin ( m x ) cos ( n x ) d x .

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Integrate y = tan x sec 4 x .

tan ( x ) x ( 8 tan x 21 + 2 7 sec x 2 tan x ) + C = f ( x )

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For each pair of integrals, determine which one is more difficult to evaluate. Explain your reasoning.

sin 456 x cos x d x or sin 2 x cos 2 x d x

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tan 350 x sec 2 x d x or tan 350 x sec x d x

The second integral is more difficult because the first integral is simply a u -substitution type.

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Practice Key Terms 2

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Source:  OpenStax, Calculus volume 2. OpenStax CNX. Feb 05, 2016 Download for free at http://cnx.org/content/col11965/1.2
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