linear equations:
* 5xy = 2
* y + x = 4x + 5
* y = 3x + x^2
* y = 4(x - 1)
* 10y = 4x
* 5y = 2x
* y = 4.7
* y = 2/5x
* 2x + 3y = 7
* y = x + 5
* y = 4/x
* 4x/3
* y = 1 - x^2
* y = -3x
* y = 5 - 4x
* y = 2 + 5x^2
* y = 1/2x - 4
* y = 4.3x - 2
* y = 9 + 3x
* y = 9 - 3.5x
* y = -x^2 - 5
* y = -2/x
* y = 1/x
* y = -x
* y = -2/5x
nonlinear equation:
* y = πx
