Video Transcript
Solve 20 is equal to 50 multiplied
by 1.029 to the power of 𝑥 for 𝑥, giving your answer to three decimal places.
In order to calculate the exponent
of any exponential function, we will need to use logarithms. Before doing this in this question,
we will divide both sides of the equation by 50. The left-hand side simplifies to
two-fifths. As a decimal, this is equal to
0.4. On the right-hand side, the 50s
cancel. So, we are left with 1.029 to the
power of 𝑥.
There are two ways of approaching
the problem from this point. Firstly, we could recall that if 𝑎
to the power of 𝑥 is equal to 𝑏, then 𝑥 is equal to log base 𝑎 of 𝑏. In our question, 𝑎 is equal to
1.029 and 𝑏 is equal to 0.4. This means that 𝑥 is equal to log
to the base 1.029 of 0.4. Typing this into the calculator
gives us negative 32.052194 and so on. As we need to give our answer to
three decimal places, the one is the deciding number. As this is less than five, 𝑥 is
equal to negative 32.052 to three decimal places. We could check this answer by
substituting our value of 𝑥 into the original equation.
An alternative method from the line
0.4 is equal to 1.029 to the power of 𝑥 would be to take logs of both sides. We could then use one of our laws
of logarithms to simplify the right-hand side. log 𝑎 to the power of 𝑥 is equal to
𝑥 multiplied by log 𝑎. The right-hand side simplifies to
𝑥 multiplied by log of 1.029. Dividing both sides of the equation
by this gives us 𝑥 is equal to log 0.4 divided by log of 1.029. Once again, this gives us negative
32.052 to three decimal places.
