x → 2 lim 1 2 6 x 4 − 1 0 0 8 x 3 + 3 0 2 4 x 2 − 4 0 3 2 x + 2 0 1 6 6 3 x 5 − 6 3 0 x 4 + 2 5 2 0 x 3 − 5 0 4 0 x 2 + 5 0 4 0 x − 2 0 1 6 = ?
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Congratulations, :) (+1) Nice solution.
Using L'Hospital's Rule (I simply insist):
x → 2 lim 1 2 6 x 4 − 1 0 0 8 x 3 + 3 0 2 4 x 2 − 4 0 3 2 x + 2 0 1 6 6 3 x 5 − 6 3 0 x 4 + 2 5 2 0 x 3 − 5 0 4 0 x 2 + 5 0 4 0 x − 2 0 1 6 [ 0 0 ] = L’H x → 2 lim 5 0 4 x 3 − 3 0 2 4 x 2 + 6 0 4 8 x − 4 0 3 2 3 1 5 x 4 − 2 5 2 0 x 3 + 7 5 6 0 x 2 − 1 0 0 8 0 x + 5 0 4 0 [ 0 0 ] = L’H x → 2 lim 1 5 1 2 x 2 − 6 0 4 8 x + 6 0 4 8 1 2 6 0 x 3 − 7 5 6 0 x 2 + 1 5 1 2 0 x − 1 0 0 8 0 [ 0 0 ] = L’H x → 2 lim 3 0 2 4 x − 6 0 4 8 3 7 8 0 x 2 − 1 5 1 2 0 x + 1 5 1 2 0 [ 0 0 ] = L’H x → 2 lim 3 0 2 4 7 5 6 0 x − 1 5 1 2 0 = 3 0 2 4 7 5 6 0 ( 2 ) − 1 5 1 2 0 = 3 0 2 4 1 5 1 2 0 − 1 5 1 2 0 = 0
Yes, L'Hospital's Rule can solve the problem. You wrote a good solution too ! Thanks you very much ! However, I used alternative method.
Haha neat and eccentric (+1)
Let the numerator be p ( x ) and the denominator be q ( x ) . Use Horner's Method to rewrite them as polynomials in ( x − 2 ) :
\(\displaystyle\begin{align} p(x):&& \begin{array}{rrrrrr} 63 & -630 & 2520 & -5040 & 5040 & -2016 \\ \fbox{2} & 126 & -1008 & 3024 & -4032 & 2016 \\ \hline 63 & -504 & 1512 & -2016 & 1008 & \boxed{0:=p_0} \\ \fbox{2} & 126 & -756 & 1512 & -1008 & \\ \hline 63 & -378 & 756 & -504 & \boxed{0=:p_1} & \\ \fbox{2} & 126 & -504 & 504 & & \\ \hline 63 & -252 & 252 & \boxed{0=:p_2} & & \\ \fbox{2} & 126 & -252 & & & \\ \hline 63 & -126 & \boxed{0=:p_3} & & & \\ \fbox{2} & 126 & & & & \\ \hline \boxed{63=:p_5} & \boxed{0=:p_4} & & & & \end{array},&& p(x)=\sum_{k=0}^5p_k(x-2)^k=63(x-2)^5\\\\
q(x):&& \begin{array}{rrrrr} 126 & -1008 & 3024 & -4032 & 2016\\ \fbox{2} & 252 & -1512 & 3024 & -2016\\ \hline 126 & -756 & 1512 & -1008 & \boxed{0 =: q_0}\\ \fbox{2} & 252 & -1008 & 1008 & \\ \hline 126 & -504 & 504 & \boxed{0 =: q_1} &\\ \fbox{2} & 252 & -504 & & \\ \hline 126 & -252 & \boxed{0 =: q_2} & &\\ \fbox{2} & 252 & & & \\ \hline \boxed{126 =: p_4} & \boxed{0 =: q_3} & & & \end{array}, && q(x)=\sum_{k=0}^4 q_k(x-2)^k=126(x-2)^4 \end{align} \)
Putting all together: x → 2 lim q ( x ) p ( x ) = x → 2 lim 1 2 6 ( x − 2 ) 4 6 3 ( x − 2 ) 5 = x → 2 lim 2 x − 2 = 0
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lim x → 2 1 2 6 x 4 − 1 0 0 8 x 3 + 3 0 2 4 x 2 − 4 0 3 2 x + 2 0 1 6 6 3 x 5 − 6 3 0 x 4 + 2 5 2 0 x 3 − 5 0 4 0 x 2 + 5 0 4 0 x − 2 0 1 6
= lim x → 2 1 2 6 ( x 4 − 8 x 3 + 2 4 x 2 − 3 2 x + 1 6 ) 6 3 ( x 5 − 1 0 x 4 + 4 0 x 3 − 8 0 x 2 + 8 0 x − 3 2 )
= lim x → 2 1 2 6 ( x 4 + 4 ( − 2 ) x 3 + 6 ( − 2 ) 2 x 2 + 4 ( − 2 ) 3 x + ( − 2 ) 4 ) 6 3 ( x 5 + 5 ( − 2 ) x 4 + 1 0 ( − 2 ) 2 x 3 + 1 0 ( − 2 ) 3 x 2 + 5 ( − 2 ) 4 x + ( − 2 ) 5 )
= lim x → 2 1 2 6 ( x − 2 ) 4 6 3 ( x − 2 ) 5 (Binomial Theorem)
= lim x → 2 2 ( x − 2 )
= 2 0
= 0
L'Hospital's Rule is not involved. Ha!