Math Problem Statement

Find the limit as x goes to 0 of the function sin2x/sin4x using the double angle identity

Solution

To find the limit of the function limx0sin(2x)sin(4x)\lim_{{x \to 0}} \frac{\sin(2x)}{\sin(4x)} using the double angle identity, let's start by applying the double angle identities for sine:

sin(2x)=2sin(x)cos(x)\sin(2x) = 2\sin(x)\cos(x) sin(4x)=2sin(2x)cos(2x)\sin(4x) = 2\sin(2x)\cos(2x)

Now, substitute sin(2x)\sin(2x) in the denominator:

sin(2x)sin(4x)=2sin(x)cos(x)2sin(2x)cos(2x)\frac{\sin(2x)}{\sin(4x)} = \frac{2\sin(x)\cos(x)}{2\sin(2x)\cos(2x)}

Simplifying by canceling the common factor of 2:

sin(2x)sin(4x)=sin(x)cos(x)sin(2x)cos(2x)\frac{\sin(2x)}{\sin(4x)} = \frac{\sin(x)\cos(x)}{\sin(2x)\cos(2x)}

Now, substitute the expression sin(2x)\sin(2x) again:

sin(x)cos(x)2sin(x)cos(x)cos(2x)=12cos(2x)\frac{\sin(x)\cos(x)}{2\sin(x)\cos(x)\cos(2x)} = \frac{1}{2\cos(2x)}

Taking the limit as x0x \to 0:

limx012cos(2x)=12cos(0)=12×1=12\lim_{{x \to 0}} \frac{1}{2\cos(2x)} = \frac{1}{2\cos(0)} = \frac{1}{2 \times 1} = \frac{1}{2}

So, the limit is:

limx0sin(2x)sin(4x)=12\lim_{{x \to 0}} \frac{\sin(2x)}{\sin(4x)} = \frac{1}{2}

Would you like more details or have any questions?

Here are 5 related questions:

  1. What is the limit of limx0sin(3x)sin(5x)\lim_{{x \to 0}} \frac{\sin(3x)}{\sin(5x)}?
  2. How does L'Hôpital's Rule apply to trigonometric limits?
  3. What is the Taylor series expansion for sin(x)\sin(x) near x=0x = 0?
  4. How do you evaluate limits involving sine and cosine functions using their small-angle approximations?
  5. What is the limit limx01cos(x)x2\lim_{{x \to 0}} \frac{1 - \cos(x)}{x^2} and how is it derived?

Tip: For small angles, the sine function can be approximated by sin(x)x\sin(x) \approx x, which is useful in limit problems.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Limits
Double Angle Identity

Formulas

Double angle identities for sine

Theorems

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Suitable Grade Level

College Level