Answer:
θ1 = 33.38°
Step-by-step explanation:
From Snell's law of refraction,
n1•sinθ1 = n2•sinθ2
We are given ;
Angle of refraction; θ2 = (90 - 26.4°) = 63.6°
Index of refraction; n1 = 1.628
Index of refraction in air; n2 will have a constant value of 1
Now, we are looking for angle of incidence θ1, so let's make θ1 the subject;
n1•sinθ1 = n2•sinθ2
So, sinθ1 = (n2•sinθ2)/n1
Plugging in the relevant values;
sinθ1 = (1 x sin 63.6)/1.628
sinθ1 = 0.5502
θ1 = sin^(-1)0.5502
θ1 = 33.38°