Solution :
The value of sec 90 degrees is ∞ or not defined.
Proof :
∠ A of Δ ABC is made large and large until it becomes 90 degrees. As ∠ A gets large and large ∠ C gets smaller and smaller. Side AB goes on decreasing. The point A gets closer to point B. When ∠ C becomes very close to 0 degree. The side AC almost coincide with side BC and side AB becomes to zero.
So, AC = BC and AB = 0
By using trigonometric formulas,
sec90∘ = hypotenusebase = hb
sec90∘ = ACAB = AC0 = ∞ or not defined
Hence, the value of sec90∘ = ∞ or not defined.