Factorise: 8+(b^2-2)^4-6(b^2-2)^2

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¯¯¯¯¯¯¯¯)?

How do i do this? i don’t understand

Me with this one question, and i'll upvote the brainliest answer