We express everything in terms of `sin y` and `cos y` and then simplify.

("LHS" stands for "left-hand side" of the equation and "RHS" means "right-hand side".)

`"LHS"=tan\ yxx1/(sin y)`

`=(sin y)/(cos y)xx1/(sin y)`

`=1/(cos y)`

`=sec\ y`

`="RHS"`

Please support IntMath!