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calculate limit
+1
vote
169
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$\lim_{x\rightarrow \infty }\left(4^{x}+5^{x}\right)^{1/x}$
calculus
limits
asked
Jul 11, 2015
in
Calculus
by
saket nandan
Active
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5.1k
points)
retagged
Aug 2, 2015
by
Arjun

169
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answer
comment
0
if we take 4 common instead of 5 then ans becomes 4 then how we can decide the answer
0
no, answer is 5 only. We can't take 4 out as then the term inside becomes $\infty^0$.
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3
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Best answer
$\lim_{x \to \infty} (4^x+5^x)^\frac{1}{x} = \lim_{x \to \infty} \left(5^x \left((\frac{4}{5})^x +1\right )\right)^\frac{1}{x}\\ =\lim_{x \to \infty} 5\times( )^{\frac{1}{\infty}} \text {(the term inside () ranges between 1 and 2)} \\ =5\times()^0\\ =5\times1\\=5$
answered
Aug 4, 2015
by
Salman
Junior
(
985
points)
selected
Nov 28, 2015
by
Arjun
comment
0
() can be anything?
+1
Since the power is zero, it will be always equal to 1.
0
So, 0^0 = 1 rt?
+1
Sorry, Mistake.
Thanks for pointing out,
$\left(\frac{4}{5} \right )^\infty + 1 \neq 0$
Since $\left( \frac{4}{5}\right)^\infty > 0$
+1
Actually you were correct. $0^0 = 1$.
Ref:
http://mathforum.org/library/drmath/view/69917.html
+1
Didn't knew that. Thanks for the reference.
0
(4/5)∞ wil always be 0.
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+1
vote
very easy
lt>inf (4^x+5^x)^1/x
lt>inf 5^x*1/x[(4/5)^x +1]^1/x
ans will be 5
since 4/5 will give <1 no. and its to the power inf will results 0
answered
Jul 15, 2015
by
anmolgate
(
269
points)
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0
votes
$\bf{\displaystyle \lim_{x\rightarrow \infty} \left(4^x+5^x \right) \approx \lim_{x\rightarrow \infty}5^x}$
$\bf{So\; \displaystyle \lim_{x\rightarrow \infty} \left(4^x+5^x \right)^{\frac{1}{x}} \approx \lim_{x\rightarrow}\left(5\right)^{\frac{x}{x}} = 5.}$
answered
Nov 24, 2015
by
Jagdish Singh
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521
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