A student spends the same amount each week for bus fare. In 6 weeks, he spends $81. Which equation shows this relationship? Let
2 answers:
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Answer:
1. leave the radical symbol and don't try to convert it to a decimal form
2. The approximated value differs from the exact solution and doesn't give a true equation.
3. Depending on the case, if she needs a mathematical answer, the exact value should be used, but for more practical applications, the rounded decimal form would be more usable.
Step-by-step explanation:
The step by step solution to the equation:
1.- Exact solution means that if in the final step when solving for x the value of is not a perfect cube, one needs to leave it indicated as a radical expression (with the radical symbol).
in our case, the cubic root of 189 is not a perfect cube. The factor form of 189 is: , so there is a perfect cube factor (
), but the other factor (7) is a prime number. Therefore 3 can get out of the root, while 7 stays inside.
2.- The equation was solved above, in exact form. Now to solve it giving a decimal approximation, we use a calculator to find the cubic root of 7, which is an irrational number with infinite number of decimals, the first of which we type here:
Therefore, the decimal approximation to the solving for x would be:
Where we rounded to two decimals as requested.
When we replace the exact answer in the original expression, we get a perfect equality:
While if we use the approximate answer, we get:
which is NOT a true equality.
3.- I would stick with the idea of showing the exact answer as answer to the mathematical equation. but for a practical case (for example she needs to by some material as a result of her equation solving, it would be more practical to take the numerical approximation to the store, instead of a cubic root of a number.