How many basic types of periodontal disease have been identified by the american academy of periodontology?

Subtract 8 1/6 - 4 5/6 . simplify the answer and write as a mixed number.

Which expression is equivalent to (3^2)^-2 a.-81 b.-12 c.1/81 d.1/12

Arley is building a model of a city map. in one part of the city, three roads form a right triangle, which harley draws as triangle abc, with the following measures: m∠b=90° and m∠a=30°. in his scale model, the hypotenuse of triangle abc, ac¯¯¯¯¯¯¯¯, has a length of 817−−√ cm. what is the value of a (the length of bc¯¯¯¯¯¯¯¯)?