MHB Who can give me a hint of how to calculate this integral,Thanks

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The integral discussed is $$\int_{0}^{\frac{-a}{2}+\frac{\sqrt{392-{a}^{2}}}{2}} {y}^{2}\arcsin\left({\frac{a+y}{\sqrt{196-{y}^{2}}}}\right)\,dy$$, which lacks an explicit evaluation but has interesting numerical solutions. Users suggest using GNU Octave or PTC Mathcad Prime 3.0 for calculations and visualizations. The GNU Octave code provided allows for numerical integration and plotting of the function. There is curiosity about the underlying formula for the curve represented by the integral. Overall, the discussion emphasizes numerical methods and software tools for evaluating complex integrals.
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$$\int_{0}^{\frac{-a}{2}+\frac{\sqrt{392-{a}^{2}}}{2}} {y}^{2}\arcsin\left({\frac{a+y}{\sqrt{196-{y}^{2}}}}\right)\,dy$$
 

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I'm not seeing an explicit evaluation, but I found the numerical solutions fascinating:View attachment 7762
 

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tkhunny said:
I'm not seeing an explicit evaluation, but I found the numerical solutions fascinating:

Thanks very much. Could you tell me which software did you use to express this curve? Is there a formula for this curve. Thanks again for your help.
 
zhaojx84 said:
Thanks very much. Could you tell me which software did you use to express this curve? Is there a formula for this curve. Thanks again for your help.

Hi zhaojx84, welcome to MHB! (Wave)

In GNU Octave, the free version of MatLab, we can do:
Code:
f = @(a, y) y^2 * asin((a + y) / (sqrt(196 - y^2)));
g = @(a) quad(@(y) f(a, y), 0, (-a / 2 + (sqrt(392 - a^2)) / 2));
x = -11:0.2:14;
y = arrayfun(g, x);
plot(x, y);

In Octave Online, we can quickly see what it does.

View attachment 7768
 

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zhaojx84 said:
Thanks very much. Could you tell me which software did you use to express this curve? Is there a formula for this curve. Thanks again for your help.
I used PTC Mathcad Prime 3.0

It required pretty much what you see. Just type in what you want. The algebraic interpretation is provided.
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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