Tag Archives: Math

Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1, Problem 7

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PROBLEM:

A right circular cylinder, a radius of base xx, height yy, is inscribed in a right circular cone, radius of base rr and a height hh. Express yy as a function of xx (rr and hh are constants).

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SOLUTION:

Refer to the figure below for an elevation view.

Schematic Diagram of a right circular cylinder inscribed in a right circular cone.
Diagram of a right circular cylinder with a base radius of r and height y inscribed in a right circular cone with base radius r and height h.

By ratio and proportion of two similar triangles, we have

yr−x=hry=h(r−x) r  (Answer)\begin{align*} \frac{y}{r-x} & = \frac{h}{r} \\ y & =\frac{h\left(r-x\right)\:}{r} \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right) \\ \end{align*}
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Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1 Problem 6

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PROBLEM:

The stiffness of a beam of rectangular cross-section is proportional to the breadth and the cube of the depth. If the breadth is 20 cm, express the stiffness as a function of the depth.

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SOLUTION:

Let SS=stiffness, bb=breadth, and dd=depth

S=bd3S=20d3  (Answer)\begin{align*} S & =bd^3 \\ S & = 20 d^3 \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right) \end{align*}
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Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1 Problem 5

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PROBLEM:

Express the area AA of an equilateral triangle as a function of its side xx.

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SOLUTION:

From the formula of the area of a triangle, A=12absin⁡(θ)\displaystyle A=\frac{1}{2} \text{a}\text{b} \sin\left(\theta \right). Also, we know that the interior angle of an equilateral triangle is 60 degrees, and sin⁡ 60∘=32\displaystyle \sin\:60^{\circ} =\frac{\sqrt{3}}{2}.

A=12absin⁡(θ)A=12⋅x⋅x⋅sin⁡ 60∘A=12⋅x2⋅32A=34x2  (Answer)\begin{align*} A & =\frac{1}{2} \text{a}\text{b} \sin\left(\theta \right) \\ A & =\frac{1}{2} \cdot x\cdot x\cdot \sin\:60^{\circ} \\ A & =\frac{1}{2}\cdot x^2\cdot \frac{\sqrt{3}}{2} \\ A & =\frac{\sqrt{3}}{4}x^2 \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right) \\ \end{align*}
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Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1 Problem 4

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PROBLEM:

Express the distance DD traveled in tt hr by a car whose speed is 60 km/hr.

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SOLUTION:

Distance=Rate×TimeD=(60 km/hr)⋅t hrD=60t km  (Answer)\begin{align*} \text{Distance} & = \text{Rate} \times \text{Time} \\ D & =\left(60\:\text{km/hr} \right)\cdot t \ \text{hr} \\ D & =60t \ \text{km} \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right)\\ \end{align*}
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Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1 Problem 3

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PROBLEM:

If y=tan⁡(x+π) \displaystyle y= \tan\left(x+\pi \right), find xx as a function of yy.

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SOLUTION:

y=tan⁡(x+π)x+π=tan⁡−1yx=tan⁡−1y−π  (Answer)\begin{align*} y & = \tan\left(x+\pi \right) \\ x+\pi & = \tan^{-1}y \\ x & = \tan^{-1}y-\pi \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right)\\ \end{align*}
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Differential and Integral Calculus by Feliciano and Uy, Exercise 1.1, Problem 2

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PROBLEM:

If y=x2+3x\displaystyle y=\frac{x^2+3}{x}, find xx as a function of yy.

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SOLUTION:

y=x2+3xxy=x2+3x2−xy+3=0\begin{align*} y & = \frac{x^2+3}{x} \\ xy & =x^2+3 \\ x^2-xy+3&=0 \end{align*}

Solve for xx using the quadratic formula. We have a=1, b=−y, and c=3 a=1,\:b=-y,\:\text{and}\:c=3

x=−b±b2−4ac 2ax=−(−y)±(−y)2−4(1)(3)2(1)x=y±y2−122  (Answer)\begin{align*} x & =\frac{-b\pm \sqrt{b^2-4ac}\:}{2a} \\ x & =\frac{ -\left(-y\right)\pm \sqrt{\left(-y\right)^2-4\left(1\right)\left(3\right)}}{2\left(1\right)} \\ x & =\frac{y\pm \sqrt{y^2-12}}{2} \ \qquad \ \color{DarkOrange} \left( \text{Answer} \right) \end{align*}
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