MHB 15.2.78 But it asks for a double integral

Click For Summary
The discussion focuses on calculating the area of the region bounded by the curves y=4+4sin(x) and y=4-4sin(x) over the interval [0, π] using a double integral. Participants note that while the problem could be solved more simply with a single integral, it specifically requests a double integral format. The suggested double integral is expressed as ∫₀^π ∫₄⁻⁴sin(x)⁴⁺⁴sin(x) dy dx. This approach maintains the formal requirement of a double integral while effectively simplifying to a single integral calculation. The discussion highlights the nuances of interpreting integral types in mathematical problems.
karush
Gold Member
MHB
Messages
3,240
Reaction score
5
Use double integral to compute the area of the region
bounded by $y=4+4\sin{x}$ and $y=4-4\sin{x}$
on the interval $\left[0,\pi\right]$

View attachment 7253

ok it looks easier to do this in one $\int$ but it asks for a double $\int\int$ so ?
 

Attachments

  • 15.2.78.PNG
    15.2.78.PNG
    1.3 KB · Views: 107
Physics news on Phys.org
Re: 15.2.78 but it asks for a double integral

karush said:
Use double integral to compute the area of the region
bounded by $y=4+4\sin{x}$ and $y=4-4\sin{x}$
on the interval $\left[0,\pi\right]$
ok it looks easier to do this in one $\int$ but it asks for a double $\int\int$ so ?
$$\int_0^\pi\int_{4-4\sin x}^{4+4\sin x}dy\,dx$$ Okay, it's just a single integral in disguise, but formally it's a double integral.
 
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)}...

Similar threads

  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 20 ·
Replies
20
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K