### Video Transcript

Find the value of cos ๐ต.

Looking at this triangle, thereโs a
few things we can note. The large triangle on the outside is
an isosceles triangle, and both of the smaller interior triangles are right
triangles. The line ๐ด๐ท creates the height of
the outer isosceles triangle. It also tells us something
else. Line ๐ด๐ท creates a perpendicular
line to line ๐ถ๐ต. And that means that it bisects line
๐ถ๐ต. Line ๐ถ๐ต can be broken up into two
equal halves, both equal to 15 centimeters.

Cos of ๐ต can be found by looking
at this interior right triangle. When weโre dealing with right
triangle trig, cos of ๐ equals the adjacent side length over the hypotenuse side
length. Cos of ๐ต must equal its adjacent
side length, 15, over its hypotenuse side length, 34. Cos of angle ๐ต equals 15 over
34.