Evaluate the definite integral

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SUMMARY

The discussion focuses on evaluating the definite integral of the function \(\int \sin(3t) dt\) with boundaries from \(0\) to \(\frac{\pi}{3}\). The correct approach involves recognizing that the integral of \(\sin(nx)\) is given by the formula \(-\frac{\cos(nx)}{n} + C\). A substitution \(x = 3t\) leads to \(dt = \frac{1}{3}dx\), clarifying the integration process. The initial confusion stemmed from incorrectly stating that \(dt = 3\), which is not valid in differential calculus.

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jimen113
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[SOLVED] Evaluate the definite integral

1. Homework Statement
\int Sin(3t) dt; the boundaries are Pi/3 and zero.

Homework Equations





The Attempt at a Solution


3-cos(pi/3)^{}2-cos(0)= not the correct answer.
Help!
 
Last edited:
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Do a substitution: x = 3t. if you do that, then what does dt = ?
Plug x in, what's the integral of sinx?
 
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?
 
jimen113 said:
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?
There is no substitution required (although that would yield the same answer).
Just look at the general integration formula for Sine:
\int\sin nx\dx=- \frac{\cos nx}{n} + \mbox{Constant}
Can you get the answer now?
 
jimen113 said:
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?

If x= 3t, then dx= 3dt so dt= (1/3)dx. "dt= 3" doesn't make any sense- a differential is not a number!
 
Thank you HallsofIvy, Reshma, & Izkelley for your help. I realized my mistake was: "dt=3"
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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