### Video Transcript

Which of the following is a formula
that can be used to find the area of a triangle? A) one-half ππ cos πΆ, B)
one-half ππ sin πΆ, C) one-third ππ sin πΆ, D) one-fourth ππ cos πΆ, or E)
one-fourth ππ sin πΆ.

If we sketch a triangle and label
it π΄, π΅, and πΆ, the side length opposite vertex π΄ is usually labelled with a
lower case π. The side length opposite vertex π΅
is labelled with a lower case π. And we label lower case π the side
length opposite vertex πΆ. We have to remember that a triangle
is half of a rectangle. And so, itβs unlikely that options
C through E would be the answer.

We noticed that options A and B are
dealing with the angle at vertex πΆ, thatβs this angle, and the lengths π and
π. At this point, we recognize that we
have two sides and an included angle. And we know that the height of this
triangle will be equal to π times the sin of πΆ. To use trigonometry to solve for
the area of a triangle, we take one-half times π times π times sin of πΆ, which is
option B here.