mathinschool.com
numbers and algebraic expressions
logic, sets, intervals
absolute value
function and its properties
linear function
quadratic function
polynomials
rational function
exponential function
logarithm
number sequences
limits of sequences and functions
derivative and integral of functions
trigonometry
plane geometry
analytic geometry
solid geometry
combinatorics
probability
elements of statistics
kropki game

Draw an angle α in xy-plane. On second arm choose point P = (x,y) with distance r from origin. sinα = y/r, cosα = x/r, tanα = y/x, cotα = x/y. r = square root of (x^2 +y^2). With this definition there can calculate the trigonometric function for angles greater than 90°. There is impossible with this definition.