math - ruby diagonal of a rectangle -

i trying create method returns length of rectangle/square diagonal float. however, method diagonal doesn't seem work intended. guess have hit road block , see if of had idea on how approach problem.

class rectangle    def initialize(width, length)     @width  = width     @length = length   end    def perimeter     2*(@length + @width)   end    def area       @length * @width   end    def diagonal     # measure = math.hypot(@length, @width)     measure = (@length.to_f ** 2) + (@width.to_f ** 2)     measure.hypot(@length, @width)   end  end 

the trouble seems here:

def diagonal     # measure = math.hypot(@length, @width)     measure = (@length.to_f ** 2) + (@width.to_f ** 2)     measure.hypot(@length, @width) end 

you seem begin try calculate length using pythagoras' method, attempt call hypot method on float. have 2 options:

def diagonal   math.hypot(@length, @width) end 

or

def diagonal     math.sqrt((@length.to_f ** 2) + (@width.to_f ** 2)) end