Video Transcript
Simplify sin 𝛼 over one plus tan
𝛼 minus sin two 𝛼 over two cos 𝛼 plus two sin 𝛼.
So I’ve copies down the expression
to simplify, and my goal first of all is to get everything in terms of sin 𝛼 and
cos 𝛼. That means rewriting tan 𝛼 as sin
𝛼 over cos 𝛼 and sin two 𝛼 as two times sin 𝛼 times cos 𝛼, where here we used
the double angle identity for sine.
Okay so now we have something in
terms of only sin 𝛼 and cos 𝛼. Let’s simplify. We multiply the first fraction by
cos 𝛼 over cos 𝛼 in an attempt to simplify the denominator. And of course because cos 𝛼 over
cos 𝛼 is just one, this doesn’t change the value of the fraction.
So now the first fraction is sin 𝛼
cos 𝛼 over cos 𝛼 plus sin 𝛼. Is there anything we can do to
simplify the second fraction before we perform the subtraction? Yes, the numerator and denominator
have a common factor of two, which we can cancel out. So we are left with sin 𝛼 cos 𝛼
over cos 𝛼 plus sin 𝛼.
We can notice at least two terms of
the same, and so when we subtract one from the other, we get zero. So sin 𝛼 over one plus tan 𝛼
minus sin two 𝛼 over two cos 𝛼 plus two sin 𝛼 is simply equal to zero, and you
can’t get much simpler than that.
