- #1
FaroukYasser
- 62
- 3
Homework Statement
For $$\lim _{ x\rightarrow \infty }{ \frac { { x }^{ 2 }+{ e }^{ -{ x }^{ 2 }\sin ^{ 2 }{ x } } }{ \sqrt { { x }^{ 4 }+1 } } } $$, determine whether it exists. If it does, find its value. if it doesn't, explain.
Homework Equations
Sand witch theorem and arithmetic rule
The Attempt at a Solution
I reached that the limit is 1 using the following:
$$\lim _{ x\rightarrow \infty }{ \frac { { x }^{ 2 }+{ e }^{ -{ x }^{ 2 }\sin ^{ 2 }{ x } } }{ \sqrt { { x }^{ 4 }+1 } } } =\lim _{ x\rightarrow \infty }{ \frac { { x }^{ 2 } }{ \sqrt { { x }^{ 4 }+1 } } +\frac { 1 }{ { e }^{ { x }^{ 2 }\sin ^{ 2 }{ x } }\sqrt { { x }^{ 4 }+1 } } } \\ \frac { 1 }{ { e }^{ x } } <\frac { 1 }{ { e }^{ { x }^{ 2 } }\sqrt { { x }^{ 4 }+1 } } <\frac { 1 }{ { e }^{ { x }^{ 2 }\sin ^{ 2 }{ x } }\sqrt { { x }^{ 4 }+1 } } <\frac { 1 }{ \sqrt { { x }^{ 4 }+1 } } \\ \\ \lim _{ x\rightarrow \infty }{ \frac { 1 }{ { e }^{ x } } } =\lim _{ x\rightarrow \infty }{ \frac { 1 }{ \sqrt { { x }^{ 4 }+1 } } } =0$$
Therefore by the sandwich theorem:
$$\lim _{ x\rightarrow \infty }{ \frac { 1 }{ { e }^{ { x }^{ 2 }\sin ^{ 2 }{ x } }\sqrt { { x }^{ 4 }+1 } } } =0$$
Also,
$$\lim _{ x\rightarrow \infty }{ \frac { { x }^{ 2 } }{ \sqrt { { x }^{ 4 }+1 } } } =1$$
Hence:
$$\lim _{ x\rightarrow \infty }{ \frac { { x }^{ 2 }+{ e }^{ -{ x }^{ 2 }\sin ^{ 2 }{ x } } }{ \sqrt { { x }^{ 4 }+1 } } } =1+0=1$$
I tried to put the limit into wolfram but it gave me a time limit exceeded. Is there a reason for this? Does the limit really not exist? And is there anything wrong in my argument?
Thank you