Question

a=6-√35 find the value of a2+1/a2 how last two steps r done I can't understand

Answer 1

a² = (6 - √35)² = 36 - 12√35 + 35 = 71 - 12√35

1/a²  =    71 + 12√35    =           71  + 12√35    = 71 + 12√35

           (71)² - (12√35)²              5041 - 5040

a² + 1/a²   = 71 - 12√35 + 71 + 12√35 = 142