Question

I really don’t know how to do this

Answer 1

0.64^2 = 1- 5.2^2/a^2 a≠0
(16/25)^2= 1- (26/5)^2/a^2
256/625=1- 676/25a^2
676/25a^2=1- 256/625
676/25a^2=369/625
422500=9225a^2
a^2 = 16900/369
a= 6.76753
= 6.8

D is the answer