Need help with integration

  • #1
The integral of (sin(t)cos(t)) has two possible solutions: {(sint)^2}/2 and {-(cost)^2}/2 eventhough these two function are not same. Although these both solutions give same values for the definite integrals, different results are obtained when such integration appears when solving differential equations. I need some help to get out of this confusion and need to know how do we choose which solution we should use for a given problem
 

Answers and Replies

  • #2
Gib Z
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Indefinite integrals can vary by an additive constant (the +C at the end). The two functions you have only vary by a constant.
 
  • #3
HallsofIvy
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The integral of (sin(t)cos(t)) has two possible solutions: {(sint)^2}/2 and {-(cost)^2}/2 eventhough these two function are not same. Although these both solutions give same values for the definite integrals, different results are obtained when such integration appears when solving differential equations. I need some help to get out of this confusion and need to know how do we choose which solution we should use for a given problem
Any (indefinite) integral has an infinite number of different solutions- but they all differ by added constants. In this particular case, since [itex]sin^2(t)+ cos^2(t)= 1[/itex], [itex]cos^2(t)= 1- sin^2(t)[/itex] so [itex]-cos^2(t)/2= -(1- sin^2(t))/2= -1/2+ sin^2(t)/2[/itex]. Your two solutions differ by the constant "-1/2".
 
  • #4
Thanks a lot...... The replies were really helpful
 

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