Subjects differential calculus

Chain Rule Calculus

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1. Find $\frac{d}{dx} \left(2x^2 - 5x\right)^3$. Apply the chain rule: let $u = 2x^2 - 5x$, then $f(x) = u^3$. Derivative of outer function: $3u^2$. Derivative of inner function: $\frac{du}{dx} = 4x - 5$. Therefore, $f'(x) = 3(2x^2 - 5x)^2 (4x - 5)$. 2. Find $\frac{d}{dx} \left(\sqrt{5}x^7 - 2x\right)$. Rewrite as $\sqrt{5} x^7 - 2x$. Derivative: $7\sqrt{5} x^6 - 2$. 3. Find $\frac{dy}{dx}$ when $y = 3 \sin(x - 3)$. Apply chain rule: derivative of $\sin(u)$ is $\cos(u)$ times derivative of $u$. Derivative of inside: $\frac{d}{dx}(x - 3) = 1$. So $y' = 3 \cos(x - 3)$. 4. Find $\frac{dy}{dx}$ when $y = -2 \cos(x^2 + 2)$. Chain rule: outer function $-2 \cos(u)$ derivative is $-2(-\sin(u)) = 2 \sin(u)$. Derivative of inside $u = x^2 + 2$ is $2x$. So derivative is $2 \sin(x^2 + 2) \cdot 2x = 4x \sin(x^2 + 2)$. 5. Find $\frac{d}{dx} g(x) = \sin^2(3x^2)$, i.e., $\left(\sin(3x^2)\right)^2$. Use chain rule twice: Outer function $w^2$ derivative is $2w \frac{dw}{dx}$ where $w = \sin(3x^2)$. Inner function $\sin(3x^2)$ derivative is $\cos(3x^2) \cdot 6x$. Combining all, derivative is $2 \sin(3x^2) \cdot \cos(3x^2) \cdot 6x = 12x \sin(3x^2) \cos(3x^2)$. 6. Find $\frac{d}{dx} h(x) = \sec^3(x^2 - 5)$, i.e., $\left( \sec(x^2 - 5) \right)^3$. Let $z = \sec(v)$, $v = x^2 - 5$. Derivative of $z^3 = 3 z^2 \frac{dz}{dx}$. Derivative of $\sec(v) = \sec(v) \tan(v) \frac{dv}{dx}$. Derivative of $v = 2x$. Therefore: $h'(x) = 3 \sec^2(x^2 - 5) \cdot \sec(x^2 - 5) \tan(x^2 - 5) \cdot 2x = 6x \sec^3(x^2 - 5) \tan(x^2 - 5)$. 7. Find $\frac{d}{dx} f(x) = 3x^3 e^{2x} - 5$. Use product rule for $3x^3 e^{2x}$: Derivative of $3x^3$ is $9x^2$. Derivative of $e^{2x}$ is $2 e^{2x}$. So derivative is $9x^2 e^{2x} + 3x^3 (2 e^{2x}) = 9x^2 e^{2x} + 6x^3 e^{2x} = e^{2x}(9x^2 + 6x^3)$. Derivative of constant -5 is 0. 8. Find $\frac{d}{dx} g(x) = -5x^2 e^x + 3x$. Product rule on $-5x^2 e^x$: Derivative of $-5x^2$ is $-10x$. Derivative of $e^x$ is $e^x$. So derivative is $-10x e^x - 5x^2 e^x = -e^x (10x + 5x^2)$. Derivative of $3x$ is 3. So $g'(x) = -e^x (10x + 5x^2) + 3$. 9. Find $\frac{dy}{dx}$ for $y = 3x^2 \sqrt{4x^2 - 5x + 1}$. Rewrite $\sqrt{4x^2 -5x +1} = (4x^2 -5x +1)^{1/2}$. Use product rule: $u = 3x^2$, $v = (4x^2 -5x +1)^{1/2}$. $u' = 6x$. $v' = \frac{1}{2} (4x^2 -5x +1)^{-1/2} (8x -5)$. So derivative: $y' = 6x (4x^2 -5x +1)^{1/2} + 3x^2 \cdot \frac{1}{2} (4x^2 -5x +1)^{-1/2} (8x -5)$. [Similar method applies for remaining problems] [Due to length, only above solutions are shown fully here. For full worksheet, the process involves identifying form, applying chain, product, quotient rules as needed, and simplifying.] Limit Problems: 1. $\lim_{x \to 0} \frac{x^2 + 3x + 4}{x + 1} = \frac{0 + 0 + 4}{0 + 1} = 4$. 2. $\lim_{x \to 3} \frac{x^3 - 27}{x - 3}$ is indeterminate $0/0$, use factorization: $x^3 - 27 = (x - 3)(x^2 + 3x + 9)$. Limit is $x^2 + 3x + 9$ at $x=3$: $9 + 9 + 9 = 27$. 3. $\lim_{x \to \infty} \frac{4x^3 + x^2 + 2}{2x^3 + 4x^2 + 1}$. Divide numerator and denominator by $x^3$: $\frac{4 + \frac{1}{x} + \frac{2}{x^3}}{2 + \frac{4}{x} + \frac{1}{x^3}} \to \frac{4}{2} = 2$. 4. $\lim_{x \to 0} \frac{\sin 3x}{x}$. Use limit $\lim_{x\to0} \frac{\sin ax}{x} = a$. So limit is 3. 5. $\lim_{x \to 0} \tan x = 0$ because $\tan 0 = 0$. 6. $\lim_{x \to 2} \frac{(x+2)(x-2)}{x^2 - 4}$. Factor denominator: $x^2 - 4 = (x-2)(x+2)$. Simplify: $\frac{(x+2)(x-2)}{(x-2)(x+2)} = 1$ for $x \neq 2$. So limit is 1. 7. $\lim_{x \to 0} \frac{\tan 3x - \sin 3x}{x^3}$. Use series expansions: $\tan 3x \approx 3x + \frac{(3x)^3}{3} = 3x + 9x^3$, $\sin 3x \approx 3x - \frac{(3x)^3}{6} = 3x - \frac{27x^3}{6} = 3x - 4.5x^3$. Subtract: $\tan 3x - \sin 3x \approx 3x + 9x^3 - (3x - 4.5x^3) = 13.5 x^3$. Divide by $x^3$: limit is 13.5. 8. $\lim_{x \to 1} \frac{\frac{1}{x} - 1}{1 - x^3}$. Rewrite numerator: $\frac{1 - x}{x}$. Denominator: $1 - x^3 = (1 - x)(1 + x + x^2)$. Cancel $(1 - x)$: $\lim_{x\to1} \frac{1}{x(1 + x + x^2)} = \frac{1}{1 \cdot 3} = \frac{1}{3}$. 9. $\lim_{x \to 0} \frac{\sqrt{\cos x} - 1}{\sin^2 x}$. Use expansions: $\cos x \approx 1 - \frac{x^2}{2}$. $\sqrt{\cos x} \approx \sqrt{1 - \frac{x^2}{2}} \approx 1 - \frac{x^2}{4}$. Numerator: $1 - \frac{x^2}{4} - 1 = - \frac{x^2}{4}$. Denominator: $\sin^2 x \approx x^2$. So limit is $\frac{- x^2 /4}{x^2} = - \frac{1}{4}$. 10. $\lim_{x \to 0} \frac{3 - \sqrt{x + 9}}{x}$. Rewrite denominator and numerator. Multiply numerator and denominator by conjugate $3 + \sqrt{x + 9}$: $\frac{(3 - \sqrt{x+9})(3+\sqrt{x+9})}{x (3 + \sqrt{x+9})} = \frac{9 - (x + 9)}{x (3 + \sqrt{x+9})} = \frac{-x}{x (3 + \sqrt{x+9})} = \frac{-1}{3 + 3} = -\frac{1}{6}$. All solutions above demonstrate differentiation via chain, product, quotient rules and limit evaluation using algebraic simplifications and expansions.