Greater powers

Calculus Level 2

lim x ( 2 x 1 ) 6 ( 3 x 1 ) 4 ( 2 x + 1 ) 10 = ? \lim_{x\to\infty}\frac{(2x-1)^6 (3x-1)^4}{(2x+1)^{10}} =\,?

1 1 81 16 \frac{81}{16} 16 81 -\frac{16}{81} 9 16 \frac{9}{16}

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3 solutions

Zach Abueg
Feb 24, 2017

lim x ( 2 x 1 ) 6 ( 3 x 1 ) 4 ( 2 x + 1 ) 10 = \displaystyle \lim_{x \to\ \infty} \frac {(2x - 1)^6(3x - 1)^4}{(2x + 1)^{10}} =

lim x ( 2 x ) 6 ( 3 x ) 4 ( 2 x ) 10 = \displaystyle \lim_{x \to\ \infty} \frac {(2x)^6(3x)^4}{(2x)^{10}} =

lim x ( 2 6 ) ( x 6 ) ( 3 4 ) ( x 4 ) ( 2 10 ) ( x 10 ) = \displaystyle \lim_{x \to\ \infty} \frac {(2^6)(x^6)(3^4)(x^4)}{(2^{10})(x^{10})} =

lim x [ ( 2 6 ) ( 3 4 ) 2 10 × x 10 x 10 ] = \displaystyle \lim_{x \to\ \infty} \bigg[ \frac {(2^6)(3^4)}{2^{10}} \times \frac{x^{10}}{x^{10}} \bigg]=

lim x 3 4 2 4 = \displaystyle \lim_{x \to\ \infty} \frac {3^4}{2^4} =

lim x 81 16 = \displaystyle \lim_{x \to\ \infty} \frac {81}{16} =

81 16 \displaystyle \frac {81}{16}

Naren Bhandari
Feb 24, 2017

lim x ( 2 x 1 ) 6 ( 3 x 1 ) 4 ( 2 x + 1 ) 10 \lim_{x→∞} \frac{(2x-1)^6(3x-1)^4}{(2x+1)^{10}}

= lim x ( 2 x 1 ) 6 ( 3 x 1 ) 4 ( 2 x + 1 ) 6 ( 2 x + 1 ) 4 =\lim_{x→∞} \frac{(2x-1)^6(3x-1)^4}{(2x+1)^6(2x+1)^4}

= lim x ( 2 x 1 2 x + 1 ) 6 × ( 3 x 1 2 x + 1 ) 4 =\lim_{x→∞} \left(\frac{2x-1}{2x+1}\right)^6\times\left(\frac{3x-1}{2x+1}\right)^4

= lim x ( x ( 2 6 x ) x ( 2 + 1 x ) ) 6 × ( x ( 3 1 x ) x ( 2 + 1 x ) ) 4 =\lim_{x→∞}\left(\frac{x(2 - \frac{6}{x})}{x(2+\frac{1}{x})}\right)^6\times \left(\frac{x(3 - \frac{1}{x})}{x(2+\frac{1}{x})}\right)^4

= ( 2 0 2 + 0 ) 6 × ( 3 0 2 0 ) 4 =\left(\frac{2-0}{2+0}\right)^6\times \left(\frac{3-0}{2-0}\right)^4

= 81 16 =\boxed{\frac{81}{16}}

Simple to complex complex to compoud Easy difficult doesnot matter but to share and learn it matters

Naren Bhandari - 4 years, 3 months ago

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Yes, thats true

Md Zuhair - 4 years, 3 months ago

An easy one

Md Zuhair - 4 years, 3 months ago

L = lim x ( 2 x 1 ) 6 ( 3 x 1 ) 4 ( 2 x + 1 ) 10 Divide up and down by x 10 = lim x ( 2 1 x ) 6 ( 3 1 x ) 4 ( 2 + 1 x ) 10 = 2 6 3 4 2 10 = 81 16 \begin{aligned} L &= \lim_{x \to \infty} \frac {(2x-1)^6(3x-1)^4}{(2x+1)^{10}} & \small \color{#3D99F6} \text{Divide up and down by }x^{10} \\ &= \lim_{x \to \infty} \frac {\left(2-\frac 1x \right)^6\left(3-\frac 1x \right)^4}{\left(2 +\frac 1x \right)^{10}} \\ & = \frac {2^63^4} {2^{10}} \\ & = \boxed{\dfrac {81}{16}} \end{aligned}

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