Rewriting equations so all powers have the same base
Sometimes the
common base for an exponential equation is not explicitly shown. In these cases, we simply rewrite the terms in the equation as powers with a common base, and solve using the one-to-one property.
For example, consider the equation
We can rewrite both sides of this equation as a power of
Then we apply the rules of exponents, along with the one-to-one property, to solve for
Given an exponential equation with unlike bases, use the one-to-one property to solve it.
Rewrite each side in the equation as a power with a common base.
Use the rules of exponents to simplify, if necessary, so that the resulting equation has the form
Use the one-to-one property to set the exponents equal.
Solve the resulting equation,
for the unknown.
Solving equations by rewriting them to have a common base
Do all exponential equations have a solution? If not, how can we tell if there is a solution during the problem-solving process?
No. Recall that the range of an exponential function is always positive. While solving the equation, we may obtain an expression that is undefined.
Solving an equation with positive and negative powers
Solve
This equation has no solution. There is no real value of
that will make the equation a true statement because any power of a positive number is positive.
Sometimes the terms of an exponential equation cannot be rewritten with a common base. In these cases, we solve by taking the logarithm of each side. Recall, since
is equivalent to
we may apply logarithms with the same base on both sides of an exponential equation.
Given an exponential equation in which a common base cannot be found, solve for the unknown.
Apply the logarithm of both sides of the equation.
If one of the terms in the equation has base 10, use the common logarithm.
If none of the terms in the equation has base 10, use the natural logarithm.
Use the rules of logarithms to solve for the unknown.
Solving an equation containing powers of different bases
t he silly nut company makes two mixtures of nuts: mixture a and mixture b. a pound of mixture a contains 12 oz of peanuts, 3 oz of almonds and 1 oz of cashews and sells for $4. a pound of mixture b contains 12 oz of peanuts, 2 oz of almonds and 2 oz of cashews and sells for $5. the company has 1080
Lairene and Mae are joking that their combined ages equal Sam’s age. If Lairene is twice Mae’s age and Sam is 69 yrs old, what are Lairene’s and Mae’s ages?
