What is the negative reciprocal of 7/9

Ineed ! the person who answers and shows their work on they got the answer first will be marked the !

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¯¯¯¯¯¯¯¯)?

Find the missing factor. write your answer inexponential form.9^2=9^4×