Math Problem Statement

1. Find ∫ (x + 5x^2 + 3) / √x dx. 2. Find d³y/dx³ if y = 2sin(2x) + cos(x).

Solution

Let’s solve the two problems from the uploaded image.


1. Find x+5x2+3xdx\int \frac{x + 5x^2 + 3}{\sqrt{x}} \, dx:

We begin by rewriting the integral: x+5x2+3xdx=xxdx+5x2xdx+3xdx\int \frac{x + 5x^2 + 3}{\sqrt{x}} \, dx = \int \frac{x}{\sqrt{x}} \, dx + \int \frac{5x^2}{\sqrt{x}} \, dx + \int \frac{3}{\sqrt{x}} \, dx

Each term is simplified using the property xnxm=xnm\frac{x^n}{x^m} = x^{n-m}: xx=x112=x12,5x2x=5x212=5x32,3x=3x12\frac{x}{\sqrt{x}} = x^{1 - \frac{1}{2}} = x^{\frac{1}{2}}, \quad \frac{5x^2}{\sqrt{x}} = 5x^{2 - \frac{1}{2}} = 5x^{\frac{3}{2}}, \quad \frac{3}{\sqrt{x}} = 3x^{-\frac{1}{2}}

So the integral becomes: x12dx+5x32dx+3x12dx\int x^{\frac{1}{2}} \, dx + \int 5x^{\frac{3}{2}} \, dx + \int 3x^{-\frac{1}{2}} \, dx

Now we integrate each term using the power rule for integration xndx=xn+1n+1+C\int x^n \, dx = \frac{x^{n+1}}{n+1} + C (where n1n \neq -1):

  1. x12dx=x12+112+1=x3232=23x32\int x^{\frac{1}{2}} \, dx = \frac{x^{\frac{1}{2} + 1}}{\frac{1}{2} + 1} = \frac{x^{\frac{3}{2}}}{\frac{3}{2}} = \frac{2}{3}x^{\frac{3}{2}}
  2. 5x32dx=5x32+132+1=5x5252=525x52=2x52\int 5x^{\frac{3}{2}} \, dx = 5 \cdot \frac{x^{\frac{3}{2} + 1}}{\frac{3}{2} + 1} = 5 \cdot \frac{x^{\frac{5}{2}}}{\frac{5}{2}} = 5 \cdot \frac{2}{5}x^{\frac{5}{2}} = 2x^{\frac{5}{2}}
  3. 3x12dx=3x12+112+1=3x1212=32x12=6x12\int 3x^{-\frac{1}{2}} \, dx = 3 \cdot \frac{x^{-\frac{1}{2} + 1}}{-\frac{1}{2} + 1} = 3 \cdot \frac{x^{\frac{1}{2}}}{\frac{1}{2}} = 3 \cdot 2x^{\frac{1}{2}} = 6x^{\frac{1}{2}}

Adding them together, the result is: x+5x2+3xdx=23x32+2x52+6x12+C\int \frac{x + 5x^2 + 3}{\sqrt{x}} \, dx = \frac{2}{3}x^{\frac{3}{2}} + 2x^{\frac{5}{2}} + 6x^{\frac{1}{2}} + C


2. Find d3ydx3\frac{d^3y}{dx^3} if y=2sin(2x)+cos(x)y = 2\sin(2x) + \cos(x):

Step 1: First derivative (yy'):

y=2sin(2x)+cos(x)y = 2\sin(2x) + \cos(x)

The derivatives of sin(2x)\sin(2x) and cos(x)\cos(x) are:

  • ddx[sin(2x)]=2cos(2x)\frac{d}{dx}\big[\sin(2x)\big] = 2\cos(2x) (by the chain rule),
  • ddx[cos(x)]=sin(x)\frac{d}{dx}\big[\cos(x)\big] = -\sin(x).

So: y=ddx[2sin(2x)+cos(x)]=22cos(2x)sin(x)=4cos(2x)sin(x)y' = \frac{d}{dx}\big[2\sin(2x) + \cos(x)\big] = 2 \cdot 2\cos(2x) - \sin(x) = 4\cos(2x) - \sin(x)

Step 2: Second derivative (yy''):

y=4cos(2x)sin(x)y' = 4\cos(2x) - \sin(x)

Now differentiate term by term:

  • ddx[4cos(2x)]=4(2sin(2x))=8sin(2x)\frac{d}{dx}\big[4\cos(2x)\big] = 4 \cdot (-2\sin(2x)) = -8\sin(2x),
  • ddx[sin(x)]=cos(x)\frac{d}{dx}\big[-\sin(x)\big] = -\cos(x).

So: y=8sin(2x)cos(x)y'' = -8\sin(2x) - \cos(x)

Step 3: Third derivative (yy'''):

y=8sin(2x)cos(x)y'' = -8\sin(2x) - \cos(x)

Now differentiate again:

  • ddx[8sin(2x)]=82cos(2x)=16cos(2x)\frac{d}{dx}\big[-8\sin(2x)\big] = -8 \cdot 2\cos(2x) = -16\cos(2x),
  • ddx[cos(x)]=sin(x)\frac{d}{dx}\big[-\cos(x)\big] = \sin(x).

So: y=16cos(2x)+sin(x)y''' = -16\cos(2x) + \sin(x)


Final Answers:

  1. x+5x2+3xdx=23x32+2x52+6x12+C\int \frac{x + 5x^2 + 3}{\sqrt{x}} \, dx = \frac{2}{3}x^{\frac{3}{2}} + 2x^{\frac{5}{2}} + 6x^{\frac{1}{2}} + C
  2. d3ydx3=16cos(2x)+sin(x)\frac{d^3y}{dx^3} = -16\cos(2x) + \sin(x)

Do you want further clarification or more details?
Here are 5 related questions for further exploration:

  1. How would you evaluate definite integrals for similar functions, such as 14x+5x2+3xdx\int_1^4 \frac{x + 5x^2 + 3}{\sqrt{x}} \, dx?
  2. What is the importance of the chain rule in differentiation, as seen in the second problem?
  3. How does the power rule for integration extend to functions with fractional exponents?
  4. Can you explain how to verify the result of a third derivative using numerical methods?
  5. How would the integral change if the numerator had higher powers of xx, such as x3x^3?

Tip: Always rewrite integrals in terms of simpler powers before solving—it makes applying the power rule much easier!

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Math Problem Analysis

Mathematical Concepts

Integration
Differentiation
Power Rule for Integration
Chain Rule

Formulas

∫ x^n dx = (x^(n+1))/(n+1) + C for n ≠ -1
d/dx[sin(ax)] = a cos(ax)
d/dx[cos(ax)] = -a sin(ax)

Theorems

Power Rule for Integration
Chain Rule for Differentiation

Suitable Grade Level

Grades 11-12