Prove the trigonometric identity $\sin\left(4\right)=2\sin\left(2\right)\cos\left(2\right)$

Step-by-step Solution

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Final answer to the problem

true

Step-by-step Solution

How should I solve this problem?

  • Express everything into Sine and Cosine
  • Prove from LHS (left-hand side)
  • Prove from RHS (right-hand side)
  • Exact Differential Equation
  • Linear Differential Equation
  • Separable Differential Equation
  • Homogeneous Differential Equation
  • Integrate by partial fractions
  • Product of Binomials with Common Term
  • FOIL Method
  • Load more...
Can't find a method? Tell us so we can add it.

I. Express the LHS in terms of sine and cosine and simplify

1

Start from the LHS (left-hand side)

$\sin\left(4\right)$
2

Using the sine double-angle identity: $\sin\left(2\theta\right)=2\sin\left(\theta\right)\cos\left(\theta\right)$, where $2\theta=4$

$2\sin\left(2\right)\cos\left(2\right)$

II. Express the RHS in terms of sine and cosine and simplify

3

Start from the RHS (right-hand side)

$2\sin\left(2\right)\cos\left(2\right)$
4

Simplify $2\sin\left(2\right)\cos\left(2\right)$ using the trigonometric identity: $\sin(2x)=2\sin(x)\cos(x)$

$\frac{2\sin\left(2\cdot 2\right)}{2}$
5

Multiply $2$ times $2$

$\frac{2\sin\left(4\right)}{2}$
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Simplify the fraction $\frac{2\sin\left(4\right)}{2}$ by $2$

$\sin\left(4\right)$

III. Choose what side of the identity are we going to work on

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To prove an identity, we usually begin to work on the side of the equality that seems to be more complicated, or the side that is not expressed in terms of sine and cosine. In this problem, we will choose to work on the left side $2\sin\left(2\right)\cos\left(2\right)$ to reach the right side $\sin\left(4\right)$

$2\sin\left(2\right)\cos\left(2\right)=\sin\left(4\right)$
8

Simplify $2\sin\left(2\right)\cos\left(2\right)$ using the trigonometric identity: $\sin(2x)=2\sin(x)\cos(x)$

$\frac{2\sin\left(2\cdot 2\right)}{2}$
9

Multiply $2$ times $2$

$\frac{2\sin\left(4\right)}{2}$
10

Simplify the fraction $\frac{2\sin\left(4\right)}{2}$ by $2$

$\sin\left(4\right)$

IV. Check if we arrived at the expression we wanted to prove

11

Since we have reached the expression of our goal, we have proven the identity

true

Final answer to the problem

true

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Function Plot

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Main Topic: Trigonometric Identities

In mathematics, trigonometric identities are equalities that involve trigonometric functions and are true for every single value of the occurring variables where both sides of the equality are defined.

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