Mathematics
Grade 11
15 min
Solve logarithmic equations Set 2
Solve logarithmic equations Set 2
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1
Introduction & Learning Objectives
Learning Objectives
Apply the product, quotient, and power rules to condense logarithmic expressions within an equation.
Solve logarithmic equations by condensing terms and converting the equation to exponential form.
Solve logarithmic equations by condensing terms on both sides and applying the one-to-one property.
Identify and solve quadratic equations that arise from solving logarithmic equations.
Check all potential solutions to identify and discard extraneous solutions.
Interpret the domain restrictions of logarithmic functions in the context of equation solving.
How can we solve for the intensity of an earthquake if it's hidden inside a logarithm in the Richter scale formula? 🌋 Let's learn the techniques to unlock those variables!
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Key Concepts & Vocabulary
TermDefinitionExample
Logarithmic EquationAn equation that includes a variable within the argument of a logarithm.log₃(x + 5) = 4
Condensing LogarithmsThe process of using logarithm properties (Product, Quotient, Power Rules) to combine multiple logarithmic terms into a single logarithm.log(x) + log(2) is condensed to log(2x).
One-to-One Property of LogarithmsIf two logarithms with the same base are equal, then their arguments must also be equal.If logâ‚…(x - 1) = logâ‚…(10), then x - 1 = 10.
Extraneous SolutionA solution that is correctly derived from the algebraic steps of solving an equation, but is not a valid solution to the original equation because it violates a domain restriction.In log(x) + log(x - 3) = 1, the potential solution x = -2 is extraneous because log(-2) is undefined.
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Core Formulas
Product Rule for Logarithms
log_b(M) + log_b(N) = log_b(MN)
Use this rule to combine two logarithms with the same base that are being added into a single logarithm.
Quotient Rule for Logarithms
log_b(M) - log_b(N) = log_b(M/N)
Use this rule to combine two logarithms with the same base that are being subtracted into a single logarithm.
Power Rule for Logarithms
p * log_b(M) = log_b(M^p)
Use this rule to move a coefficient in front of a logarithm into the argument as an exponent.
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Challenging
Solve the equation: logâ‚‚(x - 1) + logâ‚‚(x + 1) = 3.
A.x = 3
B.x = 3 and x = -3
C.x = 4
D.No solution
Challenging
Find all valid solutions for the equation: log(x - 1) + log(x + 2) = log(4).
A.x = -3
B.x = 2
C.x = 2 and x = -3
D.x = 1
Challenging
For any real numbers a > 0 and b > 0, what condition must any valid solution x satisfy for the equation log(x - a) + log(x + b) = 1?
A.x > -b
B.x > a
C.x > -b or x > a
D.x > a and x > -b
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