Calculus Examples

Evaluate the Limit limit as x approaches negative infinity of ( square root of 9x^2-4)/(3x+5)
limx-9x2-43x+5limx9x243x+5
Step 1
Simplify.
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Step 1.1
Rewrite 9x29x2 as (3x)2(3x)2.
limx-(3x)2-43x+5limx(3x)243x+5
Step 1.2
Rewrite 44 as 2222.
limx-(3x)2-223x+5limx(3x)2223x+5
Step 1.3
Since both terms are perfect squares, factor using the difference of squares formula, a2-b2=(a+b)(a-b)a2b2=(a+b)(ab) where a=3xa=3x and b=2b=2.
limx-(3x+2)(3x-2)3x+5limx(3x+2)(3x2)3x+5
limx-(3x+2)(3x-2)3x+5limx(3x+2)(3x2)3x+5
Step 2
Divide the numerator and denominator by the highest power of xx in the denominator, which is -x2=xx2=x.
limx--(3x+2)(3x-2)x23xx+5xlimx(3x+2)(3x2)x23xx+5x
Step 3
Evaluate the limit.
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Step 3.1
Cancel the common factor of xx.
limx--(3x+2)(3x-2)x23+5xlimx(3x+2)(3x2)x23+5x
Step 3.2
Split the limit using the Limits Quotient Rule on the limit as xx approaches -.
limx--(3x+2)(3x-2)x2limx-3+5xlimx(3x+2)(3x2)x2limx3+5x
Step 3.3
Move the term -1 outside of the limit because it is constant with respect to x.
-limx-(3x+2)(3x-2)x2limx-3+5x
Step 3.4
Move the limit under the radical sign.
-limx-(3x+2)(3x-2)x2limx-3+5x
-limx-(3x+2)(3x-2)x2limx-3+5x
Step 4
Apply L'Hospital's rule.
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Step 4.1
Evaluate the limit of the numerator and the limit of the denominator.
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Step 4.1.1
Take the limit of the numerator and the limit of the denominator.
-limx-(3x+2)(3x-2)limx-x2limx-3+5x
Step 4.1.2
Evaluate the limit of the numerator.
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Step 4.1.2.1
Apply the distributive property.
-limx-3x(3x-2)+2(3x-2)limx-x2limx-3+5x
Step 4.1.2.2
Apply the distributive property.
-limx-3x3x+3x-2+2(3x-2)limx-x2limx-3+5x
Step 4.1.2.3
Apply the distributive property.
-limx-3x3x+3x-2+23x+2-2limx-x2limx-3+5x
Step 4.1.2.4
Simplify the expression.
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Step 4.1.2.4.1
Move x.
-limx-33xx+3x-2+23x+2-2limx-x2limx-3+5x
Step 4.1.2.4.2
Move x.
-limx-33xx+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.4.3
Multiply 3 by 3.
-limx-9xx+3-2x+23x+2-2limx-x2limx-3+5x
-limx-9xx+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.5
Raise x to the power of 1.
-limx-9x1x+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.6
Raise x to the power of 1.
-limx-9x1x1+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.7
Use the power rule aman=am+n to combine exponents.
-limx-9x1+1+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.8
Simplify by adding terms.
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Step 4.1.2.8.1
Add 1 and 1.
-limx-9x2+3-2x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.8.2
Multiply.
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Step 4.1.2.8.2.1
Multiply 3 by -2.
-limx-9x2-6x+23x+2-2limx-x2limx-3+5x
Step 4.1.2.8.2.2
Multiply 2 by 3.
-limx-9x2-6x+6x+2-2limx-x2limx-3+5x
Step 4.1.2.8.2.3
Multiply 2 by -2.
-limx-9x2-6x+6x-4limx-x2limx-3+5x
-limx-9x2-6x+6x-4limx-x2limx-3+5x
Step 4.1.2.8.3
Add -6x and 6x.
-limx-9x2+0-4limx-x2limx-3+5x
Step 4.1.2.8.4
Subtract 4 from 0.
-limx-9x2-4limx-x2limx-3+5x
-limx-9x2-4limx-x2limx-3+5x
Step 4.1.2.9
The limit at negative infinity of a polynomial of even degree whose leading coefficient is positive is infinity.
-limx-x2limx-3+5x
-limx-x2limx-3+5x
Step 4.1.3
The limit at negative infinity of a polynomial of even degree whose leading coefficient is positive is infinity.
-limx-3+5x
Step 4.1.4
Infinity divided by infinity is undefined.
Undefined
-limx-3+5x
Step 4.2
Since is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.
limx-(3x+2)(3x-2)x2=limx-ddx[(3x+2)(3x-2)]ddx[x2]
Step 4.3
Find the derivative of the numerator and denominator.
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Step 4.3.1
Differentiate the numerator and denominator.
-limx-ddx[(3x+2)(3x-2)]ddx[x2]limx-3+5x
Step 4.3.2
Differentiate using the Product Rule which states that ddx[f(x)g(x)] is f(x)ddx[g(x)]+g(x)ddx[f(x)] where f(x)=3x+2 and g(x)=3x-2.
-limx-(3x+2)ddx[3x-2]+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.3
By the Sum Rule, the derivative of 3x-2 with respect to x is ddx[3x]+ddx[-2].
-limx-(3x+2)(ddx[3x]+ddx[-2])+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.4
Since 3 is constant with respect to x, the derivative of 3x with respect to x is 3ddx[x].
-limx-(3x+2)(3ddx[x]+ddx[-2])+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.5
Differentiate using the Power Rule which states that ddx[xn] is nxn-1 where n=1.
-limx-(3x+2)(31+ddx[-2])+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.6
Multiply 3 by 1.
-limx-(3x+2)(3+ddx[-2])+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.7
Since -2 is constant with respect to x, the derivative of -2 with respect to x is 0.
-limx-(3x+2)(3+0)+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.8
Add 3 and 0.
-limx-(3x+2)3+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.9
Move 3 to the left of 3x+2.
-limx-3(3x+2)+(3x-2)ddx[3x+2]ddx[x2]limx-3+5x
Step 4.3.10
By the Sum Rule, the derivative of 3x+2 with respect to x is ddx[3x]+ddx[2].
-limx-3(3x+2)+(3x-2)(ddx[3x]+ddx[2])ddx[x2]limx-3+5x
Step 4.3.11
Since 3 is constant with respect to x, the derivative of 3x with respect to x is 3ddx[x].
-limx-3(3x+2)+(3x-2)(3ddx[x]+ddx[2])ddx[x2]limx-3+5x
Step 4.3.12
Differentiate using the Power Rule which states that ddx[xn] is nxn-1 where n=1.
-limx-3(3x+2)+(3x-2)(31+ddx[2])ddx[x2]limx-3+5x
Step 4.3.13
Multiply 3 by 1.
-limx-3(3x+2)+(3x-2)(3+ddx[2])ddx[x2]limx-3+5x
Step 4.3.14
Since 2 is constant with respect to x, the derivative of 2 with respect to x is 0.
-limx-3(3x+2)+(3x-2)(3+0)ddx[x2]limx-3+5x
Step 4.3.15
Add 3 and 0.
-limx-3(3x+2)+(3x-2)3ddx[x2]limx-3+5x
Step 4.3.16
Move 3 to the left of 3x-2.
-limx-3(3x+2)+3(3x-2)ddx[x2]limx-3+5x
Step 4.3.17
Simplify.
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Step 4.3.17.1
Apply the distributive property.
-limx-33x+32+3(3x-2)ddx[x2]limx-3+5x
Step 4.3.17.2
Apply the distributive property.
-limx-33x+32+33x+3-2ddx[x2]limx-3+5x
Step 4.3.17.3
Combine terms.
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Step 4.3.17.3.1
Multiply 3 by 3.
-limx-9x+32+33x+3-2ddx[x2]limx-3+5x
Step 4.3.17.3.2
Multiply 3 by 2.
-limx-9x+6+33x+3-2ddx[x2]limx-3+5x
Step 4.3.17.3.3
Multiply 3 by 3.
-limx-9x+6+9x+3-2ddx[x2]limx-3+5x
Step 4.3.17.3.4
Multiply 3 by -2.
-limx-9x+6+9x-6ddx[x2]limx-3+5x
Step 4.3.17.3.5
Add 9x and 9x.
-limx-18x+6-6ddx[x2]limx-3+5x
Step 4.3.17.3.6
Subtract 6 from 6.
-limx-18x+0ddx[x2]limx-3+5x
Step 4.3.17.3.7
Add 18x and 0.
-limx-18xddx[x2]limx-3+5x
-limx-18xddx[x2]limx-3+5x
-limx-18xddx[x2]limx-3+5x
Step 4.3.18
Differentiate using the Power Rule which states that ddx[xn] is nxn-1 where n=2.
-limx-18x2xlimx-3+5x
-limx-18x2xlimx-3+5x
Step 4.4
Reduce.
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Step 4.4.1
Cancel the common factor of 18 and 2.
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Step 4.4.1.1
Factor 2 out of 18x.
-limx-29x2xlimx-3+5x
Step 4.4.1.2
Cancel the common factors.
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Step 4.4.1.2.1
Factor 2 out of 2x.
-limx-29x2(x)limx-3+5x
Step 4.4.1.2.2
Cancel the common factor.
-limx-29x2xlimx-3+5x
Step 4.4.1.2.3
Rewrite the expression.
-limx-9xxlimx-3+5x
-limx-9xxlimx-3+5x
-limx-9xxlimx-3+5x
Step 4.4.2
Cancel the common factor of x.
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Step 4.4.2.1
Cancel the common factor.
-limx-9xxlimx-3+5x
Step 4.4.2.2
Divide 9 by 1.
-limx-9limx-3+5x
-limx-9limx-3+5x
-limx-9limx-3+5x
-limx-9limx-3+5x
Step 5
Evaluate the limit.
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Step 5.1
Evaluate the limit of 9 which is constant as x approaches -.
-9limx-3+5x
Step 5.2
Split the limit using the Sum of Limits Rule on the limit as x approaches -.
-9limx-3+limx-5x
Step 5.3
Evaluate the limit of 3 which is constant as x approaches -.
-93+limx-5x
Step 5.4
Move the term 5 outside of the limit because it is constant with respect to x.
-93+5limx-1x
-93+5limx-1x
Step 6
Since its numerator approaches a real number while its denominator is unbounded, the fraction 1x approaches 0.
-93+50
Step 7
Simplify the answer.
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Step 7.1
Simplify the numerator.
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Step 7.1.1
Rewrite 9 as 32.
-323+50
Step 7.1.2
Pull terms out from under the radical, assuming positive real numbers.
-133+50
-133+50
Step 7.2
Simplify the denominator.
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Step 7.2.1
Multiply 5 by 0.
-133+0
Step 7.2.2
Add 3 and 0.
-133
-133
Step 7.3
Multiply -1 by 3.
-33
Step 7.4
Divide -3 by 3.
-1
-1
 [x2  12  π  xdx ]