A calculus problem by Vighnesh Raut

Calculus Level 1

Evaluate

lim x 100 x 2 + 37 x + 90 50 x 2 + 80 x + 60 \lim _{ x\rightarrow \infty }{ \frac { 100{ x }^{ 2 }+37x+90 }{ 50{ x }^{ 2 }+80x+60 } }


The answer is 2.

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3 solutions

Vighnesh Raut
Jun 5, 2014

lim x 100 x 2 + 37 x + 90 50 x 2 + 80 x + 60 \lim _{ x\rightarrow \infty }{ \frac { 100{ x }^{ 2 }+37x+90 }{ 50{ x }^{ 2 }+80x+60 } }

= lim x 100 + 37 x + 90 x 2 50 + 80 x + 60 x 2 \lim _{ x\rightarrow \infty }{ \frac { 100+\frac { 37 }{ x } +\frac { 90 }{ { x }^{ 2 } } }{ 50+\frac { 80 }{ x } +\frac { 60 }{ { x }^{ 2 } } } }

= 100 + 0 + 0 50 + 0 + 0 \frac { 100+0+0 }{ 50+0+0 }

= 2

can anyone please suggest some other method..

Harshvardhan Mehta - 7 years ago

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hey harsh this video may help you ,especially the shortcut !! hope it helps you .

Rishabh Jain - 7 years ago

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When x-> ∞ and the highest degree of polynomial in numerator is same as the degree in denominator then simply divide the coefficient in numerator by coefficient in denominator. In this case, since the highest degree of polynomial is same, So 100/50 = 2

Hritesh Mourya - 5 years ago
Satyabrata Dash
Jun 2, 2016

lim x 100 x 2 + 37 x + 90 50 x 2 + 80 x + 60 \large\large\large\large \lim _{ x\rightarrow \infty }{ \frac { 100{ x }^{ 2 }+37x+90 }{ 50{ x }^{ 2 }+80x+60 } }

Now just divide the two Equations by x 2 x^2 ,

So , lim x 100 + 37 ( x ) + 90 x 2 50 + 80 ( x ) + 60 x 2 \large\large\large\large \lim _{ x\rightarrow \infty }{ \frac { 100+\frac { 37 }{( x) } +\frac { 90 }{ { x }^{ 2 } } }{ 50+\frac { 80 }{ (x) } +\frac { 60 }{ { x }^{ 2 } } } }

Putting x = x= \infty , we know that 1 = 0 \large\large\frac{1}{∞} \ = \ 0

So ultimately, 100 50 \large\large\frac{100}{50} = = 2 \boxed{\boxed{2}}

Hritesh Mourya
May 20, 2016

When x-> ∞ and the highest degree of polynomial in numerator is same as the degree in denominator then simply divide the coefficient in numerator by coefficient in denominator. In this case, since the highest degree of polynomial is same, So 100/50 = 2

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