The derivative of sin 3x is cos 3x. In this article, we will find the derivative of sin 3x by the substitution method, the chain rule, and the limit definition.

Table of Contents

**Derivative of sin 3x Formula**

The formula of the derivative of sin 3x is given below.

- d/dx(sin 3x) = 3cos 3x (or)
- (sin 3x)$’$ = 3 cos 3x

The following method will be used to prove the above formula.

- Derivative of sin 3x by substitution method
- Derivative of sin 3x by first principle
- Derivative of sin 3x by chain rule.

**What is the Derivative of sin 3x?**

At first, we will evaluate the derivative of sin 3x by the substitution method. We need to follow the below steps.

Step 1: Let $y=\sin 3x$

Step 2: Applying sine inverse on both sides, we have

$\sin^{-1} y =\sin^{-1} \sin 3x$

$\Rightarrow \sin^{-1} y =3x$

Step 3: Differentiating with respect to $x$, we get

$\dfrac{d}{dx}(\sin^{-1}y)=\dfrac{d}{dx}(3x)$

$\dfrac{1}{\sqrt{1-y^2}} \dfrac{dy}{dx}=\dfrac{d}{dx}(3x)$

$\Rightarrow \dfrac{1}{\sqrt{1-y^2}} \dfrac{dy}{dx}=3$

$\Rightarrow \dfrac{dy}{dx}=3\sqrt{1-y^2}$

$\Rightarrow \dfrac{dy}{dx}=3\sqrt{1-\sin^2 3x}$ $[\because y=\sin 3x]$

$\Rightarrow \dfrac{dy}{dx}=3\sqrt{\cos^2 3x}$ $[\because \sin^2 3x+\cos^2 3x=1 ]$

$\Rightarrow \dfrac{dy}{dx}=3\cos 3x$

So the derivative of sine 3x is $3\cos 3x$. That is,

\[\dfrac{d}{dx}(\sin 3x)=3\cos 3x. \quad ♣\]

Video Solution of derivative of sin 3x:

**Derivative of sin 3x by first principle**

Now, we will find the derivative of $\sin 3x$ by the first principle. Let $f(x)=\sin 3x.$ Applying the first principle of derivatives, we get that

$\dfrac{d}{dx}(f(x))$ $=\lim\limits_{h \to 0}\dfrac{f(x+h)-f(x)}{h}$

Thus the derivative of sin 3x by limit definition is equal to

$\dfrac{d}{dx}(\sin 3x)$ $= \lim\limits_{h \to 0} \dfrac{\sin 3(x+h)-\sin 3x}{h}$

$=\lim\limits_{h \to 0}\dfrac{2\cos {\frac{6x+3h}{2}} \sin {\frac{3h}{2}}}{h}$

$[\because \sin a -\sin b$ $=2\cos \frac{a+b}{2}\sin \frac{a-b}{2}]$

$=\lim\limits_{h \to 0}\cos \big(\dfrac{6x+3h}{2}\big)\cdot$ $3\cdot \dfrac{\sin \frac{3h}{2}}{3h/2}$

$=3\lim\limits_{h \to 0}\cos \big(\dfrac{6x+3h}{2}\big)$ $\lim\limits_{h \to 0}\dfrac{\sin \frac{3h}{2}}{3h/2}$

[Let 3h/2=t. Then t → 0 as h → 0]

$=3\cos \big(\dfrac{6x+0}{2}\big) \lim\limits_{t \to 0}\dfrac{\sin t}{t}$

$=3\cos 3x \cdot 1$

$=3\cos 3x$

This shows that the derivative of sin 3x is 3cos 3x which is obtained by the first principle of derivatives, that is, by the limit definition. ♣

**Also Read: **

**Derivative of root x**: The derivative of √x is 1/2√x

**Derivative of cube root of x**: The derivative of the cube root of x is 1/(3x^{2/3})

**Derivative of sin inverse x**: The derivative of sin^{-1} x is 1/√(1-x^{2})

**Integration of mod x**: The integration of |x| is -x|x|/2 +c

**Derivative of Sin 3x by chain rule**

We know that the derivative of sin x is cos x, that is, $\frac{d}{dx}(\sin x)=\cos x.$ Using this formula and by the chain rule, we will now find the derivative of sine 3x.

Recall the chain rule of derivative: $\frac{du}{dx}=\frac{du}{dz} \cdot \frac{dz}{dx},$ where $u$ is a function of $z$. To find the derivative of $\sin 3x$ by the chain rule, we put

$z=3x$

Now, $\dfrac{d}{dx}(\sin 3x)=\dfrac{d}{dx}(\sin z)$

$=\dfrac{d}{dz}(\sin z) \cdot \dfrac{dz}{dx}$ (by the chain rule)

$=\cos z \cdot 3$

$=3\cos z$

$=3\cos 3x$ $[\because z=3x]$

So the derivative of sin3x by the chain rule is equal to 3cos3x.

**FAQs on** **Derivative of Sin 3x**

**Q1: Find the derivative of sin 3x.**

Ans: The derivative of sin 3x is d/dx(sin 3x) = cos 3x d/dx(3x) = 3cos 3x.

**Q2: What is the derivative of sin**

^{2}3x?Ans: The derivative of sin^{2} 3x is 2sin(3x) cos(3x) ⋅ 3 = 3sin(6x) as we know that 2sin t cos t = sin 2t.

**Q3: Find the integration of sin 3x.**

Ans: The integration of sin 3x is ∫sin 3x dx = – (sin 3x)/3 + C where C is an integration constant.

**Q4: What is the formula of sin 3x?**

Ans: [sin 3x formula] The formula of sin 3x is sin3x = 3 sin x – 4 sin^{3} x.

**Q5: What is the derivative of sin cube x?**

Answer: The derivative of sin cube x is equal to 3sin^{2}xcosx.

This article is written by Dr. T. Mandal, Ph.D in Mathematics. On Mathstoon.com you will find Maths from very basic level to advanced level. Thanks for visiting.