Solve 4 sec sqrd x = 8

4 sec² (x) = 8

Divide each side by 4: sec² (x) = 2

Take the square root of each side: sec (x) = + or - √2

We know that sec (x) = 1/cos (x)

So the equation becomes 1/cos (x) = + or - √2

Divide '1' by each side: cos (x) = + or - (1/2) √2

x = 45°, 135°, 225°, 315°