Step-by-step explanation:

Cos 28 = 18/ y
so
y = 18 / cos 28
y = 18 /.8829
y = 20.4
Learn this...
HOY -- horizontal line, 0 slope, represented by y = a number
VUX -- vertical line, undefined slope, represented by x = a number
ok....so ur graph shows a vertical line....and a vertical line has an undefined slope
Answer:
That is the commutative property.
it is called ones period system .this is based on international system of numeration.