 That this expression should also be symmetrical about the line ' "x" = 90' rules out the possibility of choosing a linear expression in "x".Computations involving "x"(180 − "x") might immediately suggest that the expression could be of the form

A little experimentation (or by setting up and solving two linear equations in "a" and "b") will yield the values "a" = 5/4, "b" = −1/4.These give Bhaskara I's sine approximation formula.