Find the value of cos 𝐵.
Looking at this triangle, there’s 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 𝐴𝐷 creates the height of
the outer isosceles triangle. It also tells us something
else. Line 𝐴𝐷 creates a perpendicular
line to line 𝐶𝐵. And that means that it bisects line
𝐶𝐵. Line 𝐶𝐵 can be broken up into two
equal halves, both equal to 15 centimeters.
Cos of 𝐵 can be found by looking
at this interior right triangle. When we’re dealing with right
triangle trig, cos of 𝜃 equals the adjacent side length over the hypotenuse side
length. Cos of 𝐵 must equal its adjacent
side length, 15, over its hypotenuse side length, 34. Cos of angle 𝐵 equals 15 over