In addition to sine θ, cosine θ, and tangent θ,  it is useful to use the reciprocal ratios, depending on the problem. Remember, the reciprocal of a fraction is found by turning the fraction upside down.

cosecant θ is the reciprocal of sine θ

secant θ is the reciprocal of cosine θ, and

cotangent θ is the reciprocal of tangent θ

We usually write these in short form as csc θ, sec θ and cot θ. In some textbooks, "csc" is written as "cosec". But it's the same thing.

csc θ = hypotenuse / opposite

sec θ = hypotenuse / adjacent

cot θ = adjacent / opposite