Calculate the following limits:(a) limx→0sin(2x2 + x3)x ; (b) limx→0√x(sin(1/x) − cos(1/x)).
Question
Calculate the following limits:
(a) ;
(b) .
Solution
(a) limx→0sin(2x2 + x3)/x
Step 1: We can see that direct substitution will give us 0/0 which is an indeterminate form. So, we can use L'Hopital's Rule which states that the limit of a quotient of two functions as x approaches a certain value is equal to the limit of the quotients of their derivatives.
Step 2: Differentiate the numerator and the denominator.
The derivative of sin(2x2 + x3) with respect to x is (4x + 3x2)cos(2x2 + x3) using the chain rule.
The derivative of x with respect to x is 1.
Step 3: Substitute these into our limit, we get:
limx→0 (4x + 3x2)cos(2x2 + x3)
Step 4: Now, substitute x = 0 into the limit, we get:
(40 + 30^2)cos(2*0^2 + 0^3) = 0
So, limx→0sin(2x2 + x3)/x = 0
(b) limx→0√x(sin(1/x) − cos(1/x))
Step 1: Again, direct substitution will give us an indeterminate form. But in this case, L'Hopital's Rule is not applicable because we don't have a quotient of two functions.
Step 2: We can rewrite the limit as:
limx→0 √x * sin(1/x) - limx→0 √x * cos(1/x)
Step 3: Now, we can see that both of these limits are in the form 0*∞ which is an indeterminate form. We can convert this to the form 0/0 or ∞/∞ by taking the reciprocal of one of the factors.
Step 4: For the first limit, we can rewrite it as:
limx→0 (sin(1/x))/(1/√x)
Now, we can apply L'Hopital's Rule. The derivative of sin(1/x) with respect to x is -(1/x^2)cos(1/x) and the derivative of 1/√x with respect to x is -(1/2x^3/2).
Substitute these into the limit, we get:
limx→0 [-(1/x^2)cos(1/x)] / [-(1/2x^3/2)]
Simplify this, we get:
limx→0 2x^1/2 cos(1/x)
Now, substitute x = 0 into the limit, we get:
2*0^1/2 cos(1/0) = 0
Step 5: For the second limit, we can rewrite it as:
limx→0 (cos(1/x))/(1/√x)
Now, we can apply L'Hopital's Rule. The derivative of cos(1/x) with respect to x is (1/x^2)sin(1/x) and the derivative of 1/√x with respect to x is -(1/2x^3/2).
Substitute these into the limit, we get:
limx→0 [(1/x^2)sin(1/x)] / [-(1/2x^3/2)]
Simplify this, we get:
limx→0 -2x^1/2 sin(1/x)
Now, substitute x = 0 into the limit, we get:
-2*0^1/2 sin(1/0) = 0
Step 6: So, the original limit is 0 - 0 = 0.
So, limx→0√x(sin(1/x) − cos(1/x)) = 0.
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