There are a couple ways to convert from radians to degrees, but Jacob claims that he has found a new method to do this conversion that is perhaps faster than all the others. His method is simple: Given a radian measure in simplest form, substitute in for and then simplify the expression.
For example, if Jacob wanted to convert radians to degrees, he would put in place of and then simplify the numerical expression (And then, of course, label his expression with a degree symbol). You can see him use this method on the example below:
Of course, Jacob believes that his trick will work as long as is visible in the simplified expression. For example, Jacob knows he can use his trick to convert radians but not radians because no substitution can be done.
As long as is visible in the simplified expression, does Jacob's trick always work?
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Let's look at a different scenario when π is visible in the simplified expression. We've seen it used in the numerator, but what happens when π in the denominator? Does it still work?
Let's see by first converting π 1 radians into degrees the normal way (Using dimensional analysis), and then convert using Jacob's trick. If the results are not equal, Jacob's trick would no longer hold.
Like I said, let's first convert using dimensional analysis.
π 1 r a d × π r a d 1 8 0 ∘
Of course, the radian labels cancel out like common factors when multiplying fractions.
π 1 × π 1 8 0 ∘ = π 2 1 8 0 ∘
So, we know that π 1 radians is equal to π 2 1 8 0 degrees (Note that π 2 1 8 0 ∘ is equivalent to saying ( π 2 1 8 0 ) ∘ ).
Let's now try using Jacob's trick.
π 1 → ( 1 8 0 ) 1 → ( 1 8 0 1 ) ∘
So, using Jacob's trick, our answer becomes 1 8 0 1 degrees. Are the two answers equivalent?
Well, no. π 2 1 8 0 ≈ 1 8 . 2 3 8 and 1 8 0 1 ≈ 0 . 0 0 6 . So, it is quite clear that π 2 1 8 0 ∘ = 1 8 0 1 ∘ and therefore Jacob's trick doesn't always work . In fact, this trick always works when π is only on the numerator, but it doesn't usually work when π is in the denominator.