Identify Limit: Identify the limit that needs to be evaluated.We need to find the limit of the function cos(x)sin(2x) as x approaches 2π.
Direct Substitution: Direct substitution to check if the limit can be evaluated directly.If we substitute x=2π directly into the function, we get sin(π)/cos(2π). Since sin(π)=0 and cos(2π)=0, we have an indeterminate form of 0/0. This means we cannot find the limit by direct substitution.
Apply L'Hôpital's Rule: Apply L'Hôpital's Rule to evaluate the limit. L'Hôpital's Rule states that if the limit of functions f(x) and g(x) as x approaches a value c is an indeterminate form 0/0 or ∞/∞, then the limit of f(x)/g(x) as x approaches c is the same as the limit of their derivatives f′(x)/g′(x), provided this limit exists.
Differentiate Functions: Differentiate the numerator and denominator.The derivative of sin(2x) with respect to x is 2cos(2x), and the derivative of cos(x) with respect to x is −sin(x).
Apply Derivatives: Apply L'Hôpital's Rule using the derivatives.Now we need to find the limit of (2cos(2x))/(−sin(x)) as x approaches π/2.
Substitute Values: Substitute x=2π into the derivatives.Substituting x=2π into the derivatives, we get −sin(2π)2cos(π). Since cos(π)=−1 and sin(2π)=1, the expression simplifies to −12×−1 which equals 2.
Conclude Limit: Conclude the limit.The limit of cos(x)sin(2x) as x approaches 2π is 2.
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