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Without using a calculator show how you can solve for \(x\). a. \(10^{x-5}=1000\) b. \(\log (2 x+10)=2\) c. \(10^{3 x-1}=0.0001\) d. \(\log (500-25 x)=3\)

Short Answer

Expert verified
a) x = 8, b) x = 45, c) x = -1, d) x = -20

Step by step solution

01

Solve for x in 10^{x-5} = 1000

Start by expressing 1000 as a power of 10. Notice that 1000 is the same as 10^3.
02

Equate the exponents

Since the bases are the same, set the exponents equal to each other: x - 5 = 3
03

Solve for x

Add 5 to both sides of the equation to isolate x: x = 8
04

Solve for x in \log(2x + 10) = 2

Rewrite the logarithmic equation in its exponential form: 10^2 = 2x + 10
05

Simplify the equation

Calculate 10^2 to get 100: 100 = 2x + 10
06

Solve for x

Subtract 10 from both sides and then divide by 2: 2x = 90 x = 45
07

Solve for x in 10^{3x-1} = 0.0001

Express 0.0001 as a power of 10. Notice that 0.0001 is the same as 10^{-4}.
08

Equate the exponents

Since the bases are the same, set the exponents equal to each other: 3x - 1 = -4
09

Solve for x

Add 1 to both sides of the equation and then divide by 3 to isolate x: 3x = -3 x = -1
10

Solve for x in \log(500 - 25x) = 3

Rewrite the logarithmic equation in its exponential form: 10^3 = 500 - 25x
11

Simplify the equation

Calculate 10^3 to get 1000: 1000 = 500 - 25x
12

Solve for x

Subtract 500 from both sides and then divide by -25: 500 = -25x x = -20

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Exponential Equations
Exponential equations are equations where variables appear as exponents. They typically look like this: \(a^{x} = b\). To solve them, you must isolate the exponential expression and then equate the exponents if the bases are the same.

For example, in the problem \(10^{3x-1} = 0.0001\), we express 0.0001 as \(10^{-4}\). The equation becomes:\(10^{3x-1} = 10^{-4}\). Since the bases are equal, we can set the exponents equal to each other: \(3x - 1 = -4\). Then solve for \(x\) by adding 1 and dividing by 3:
\(3x = -3\)
\(x = -1\).

Remember to always check if the bases of the exponential terms can be made the same, this simplifies the equation and allows you to set the exponents equal to each other.
Logarithmic Equations
Logarithmic equations contain logarithms with variables inside them. These equations look like \(\text{log}(f(x)) = c\). To solve them, you convert the logarithmic form to its equivalent exponential form.

For instance, in \(\text{log}(2x + 10) = 2\), convert it to its exponential form: \(10^{2} = 2x + 10\), which simplifies to \(100 = 2x + 10\). Solve for \(x\) by subtracting 10 and dividing by 2:
\(100 - 10 = 2x\)
\(90 = 2x\)
\(x = 45\).

Remember, log equations often require understanding the properties of logarithms such as \(\text{log}_{b}(a) = c\) implies \(b^{c} = a\). This is the key to transforming and solving these equations.
Algebraic Manipulation
Algebraic manipulation involves rearranging and simplifying equations to isolate the variable. This includes adding, subtracting, multiplying, and dividing terms on both sides of an equation.

Take the equation \(10^{x-5} = 1000\). First, recognize that 1000 is \(10^3\). Equate the exponents: \(x - 5 = 3\). To isolate \(x\), add 5 to both sides:
\(x - 5 + 5 = 3 + 5\)
\(x = 8\).

Effective algebraic manipulation requires the use of basic algebra rules, like isolating the variable you're solving for. Practice different types of equations to become comfortable with these techniques.
Exponent Rules
Exponent rules are fundamental to solving both exponential and logarithmic equations. Here are a few important rules to remember:

* Product Rule: \(a^m \times a^n = a^{m+n}\)
* Quotient Rule: \(a^m \times a^{-n} = a^{m-n}\)
* Power Rule: \((a^m)^n = a^{mn}\)

For example, in the equation \(10^{3x-1} = 10^{-4}\), we use the fact that the bases are the same. Therefore, equate the exponents: \(3x - 1 = -4\). Solve for \(x\):
\(3x - 1 + 1 = -4 + 1\)
\(3x = -3\)
\(x = -1\).

These rules help simplify and break down complicated expressions and are integral when dealing with exponential and logarithmic functions.

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Most popular questions from this chapter

a. For any nonzero real number \(a\), what can we say about the sign of the expression \((-a)^{n}\) when \(n\) is an even integer? What can we say about the sign of \((-a)^{n}\) when \(n\) is an odd integer? b. What is the sign of the resulting number if \(a\) is a positive number? If \(a\) is a negative number? Explain your answer.

The pH scale measures the hydrogen ion concentration in a liquid, which determines whether the substance is acidic or alkaline. A strong acid solution has a hydrogen ion concentration of \(10^{-1}\) M. One \(\mathrm{M}\) equals \(6.02 \cdot 10^{23}\) particles, such as atoms, ions, molecules, etc., per liter, or 1 mole per liter. \(^{6}\) A strong alkali solution has a hydrogen ion concentration of \(10^{-14} \mathrm{M}\). Pure water, with a concentration of \(10^{-7} \mathrm{M},\) is neutral. The \(\mathrm{pH}\) value is the power without the minus sign, so pure water has a \(\mathrm{pH}\) of \(7,\) acidic substances have a pH less than \(7,\) and alkaline substances have a \(\mathrm{pH}\) greater than 7 . a. Tap water has a pH of 5.8 . Before the industrial age, rain water commonly had a pH of about \(5 .\) With the spread of modern industry, rain in the northeastern United States and parts of Europe now has a \(\mathrm{pH}\) of about \(4,\) and in extreme cases the \(\mathrm{pH}\) is about \(2 .\) Lemon juice has a \(\mathrm{pH}\) of 2.1. If acid rain with a pH of 3 is discovered in an area, how much more acidic is it than preindustrial rain? b. Blood has a pH of 7.4 ; wine has a pH of about 3.4. By how many orders of magnitude is wine more acidic than blood?

An electron weighs about \(10^{-27}\) gram, and a raindrop weighs about \(10^{-3}\) gram. How many times heavier is a raindrop than an electron? How many times lighter is an electron than a raindrop? What is the order-of- magnitude difference?

The average distance from Earth to the sun is about \(150,000,000 \mathrm{~km}\), and the average distance from the planet Venus to the sun is about \(108,000,000 \mathrm{~km}\). a. Express these distances in scientific notation. b. Divide the distance from Venus to the sun by the distance from Earth to the sun and express your answer in scientific notation. c. The distance from Earth to the sun is called 1 astronomical unit (1 A.U.) How many astronomical units is Venus from the sun? d. Pluto is \(5,900,000,000 \mathrm{~km}\) from the sun. How many astronomical units is it from the sun?

A homeowner would like to spread shredded bark (mulch) over her flowerbeds. She has three flowerbeds measuring \(25 \mathrm{ft}\) by \(3 \mathrm{ft}, 15 \mathrm{ft}\) by \(4 \mathrm{ft},\) and \(30 \mathrm{ft}\) by \(1.5 \mathrm{ft}\). The recommended depth for the mulch is 4 inches, and the shredded bark costs \(\$ 27.00\) per one cubic yard. How much will it cost to cover all of the flowerbeds with shredded bark? (Note: You cannot buy a portion of a cubic yard of mulch.)

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