MHB Find Tangent Line w/ Definite Integral - Amy's Question

AI Thread Summary
To find the equation of the tangent line to the function A(x) at x=π/2, where A(x) is defined as the definite integral from x to π/2 of sin(t)/t dt, we first determine that A(π/2) equals 0. The slope of the tangent line is found using the Fundamental Theorem of Calculus, yielding A'(x) = -sin(x)/x, which gives A'(π/2) = -2/π. With the point (π/2, 0) and the slope -2/π, the tangent line's equation is y = -2/π x + 1. This solution provides a clear method for finding tangent lines involving definite integrals.
MarkFL
Gold Member
MHB
Messages
13,284
Reaction score
12
Here is the question:

Finding tangent line with definite integral?

Find the equation of the tangent line to the graph of y=A(x) at x= pi/2, where A(x) is defined for all real x by:

A(x)= (sin t/t)dt on the integral x to pi/2

If you could show me all of the steps to finding this, I would be really happy.

Here is a link to the question:

Finding tangent line with definite integral? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.
 
Mathematics news on Phys.org
Hello Amy,

We are given the function:

$$A(x)=\int_x^{\frac{\pi}{2}}\frac{\sin(t)}{t}\,dx$$

and we are asked to find the line tangent to this function at the point:

$$\left(\frac{\pi}{2},A\left(\frac{\pi}{2} \right) \right)=\left(\frac{\pi}{2},0 \right)$$

We know $$A\left(\frac{\pi}{2} \right)=0$$ from the property of definite integrals, demonstrated here by use of the anti-derivative form of the FTOC:

$$\int_a^a f(x)\,dx=F(a)-F(a)=0$$

So, we have the point through which the tangent line must pass, now we need the slope. Using the derivative form of the FTOC, we find:

$$A'(x)=\frac{d}{dx}\int_x^{\frac{\pi}{2}}\frac{\sin(t)}{t}\,dx=-\frac{\sin(x)}{x}$$

Hence:

$$A'\left(\frac{\pi}{2} \right)=-\frac{2}{\pi}$$

We now have a point and the slope, so applying the point-slope formula, we find the equation of the tangent line is:

$$y-0=-\frac{2}{\pi}\left(x-\frac{\pi}{2} \right)$$

$$y=-\frac{2}{\pi}x+1$$

Here is a plot of $A(x)$ and the tangent line:

https://www.physicsforums.com/attachments/811._xfImport

To Amy and any other guests viewing this topic, I invite and encourage you to post other calculus questions here in our http://www.mathhelpboards.com/f10/ forum.

Best Regards,

Mark.
 

Attachments

  • amy.jpg
    amy.jpg
    11.2 KB · Views: 107
Suppose ,instead of the usual x,y coordinate system with an I basis vector along the x -axis and a corresponding j basis vector along the y-axis we instead have a different pair of basis vectors ,call them e and f along their respective axes. I have seen that this is an important subject in maths My question is what physical applications does such a model apply to? I am asking here because I have devoted quite a lot of time in the past to understanding convectors and the dual...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Back
Top