sec(2sin- 1 [3/4].
Let, sin- 1 (3/4) = t, then, sin t = 3/4.
sec(2sin- 1 [3/4] = sec(2t)
Using reciprocal identity : sec x = 1/cos x.
sec(2t) = 1/cos(2t).
Double angle formula : cos(2x) = 1 - 2sin2 x.
1/cos(2t) = 1/(1 - 2sin2 t)
= 1/(1 - 2(3/4)2)
= 1/(1 - [2*9/16])
= 1/(1 - 9/8)
= 8/(8 - 9)
= - 8.