Question 536666
Given to solve for t:
.
{{{12-e^0.4*t=3}}}
.
Get all the constants on the right side so that only the term containing the variable is on the left side. Do this by subtracting 12 from both sides to you get:
.
{{{12 - 12 - e^(0.4t) = 3 - 12}}}
.
On the left side the +12 and the -12 cancel each other out. On the right side the +3 and the -12 combine to give -9 and the equation reduces to:
.
{{{-e^(0.4t) = -9}}}
.
Multiply both sides by -1 to get:
.
{{{e^(0.4t) = 9}}}
.
Take the natural logarithm (ln) of both sides:
.
{{{ln(e^(0.4t)) = ln(9)}}}
.
Use a calculator to determine that {{{ln(9) = 2.197224577}}}. Substitute that value for the right side:
.
{{{ln(e^(0.4t)) = 2.197224577}}}
.
Now, by the rules of logarithms, the exponent can come out as a multiplier and the equation becomes:
.
{{{0.4t*ln(e) = 2.197224577}}}
.
But the value of {{{ln(e) = 1}}}. Substituting this reduces the equation to:
.
{{{0.4t = 2.197224577}}}
.
Solve for t by dividing both sides by 0.4 to get:
.
{{{t = 2.197224577/0.4}}}
.
And performing the division of the right side results in:
.
{{{t = 5.493061443}}}
.
That's the answer to the problem you were given. Hope this helps you to understand it better.
.