Is 6 ft 10 ft 12 ft a right triangle​

yes

Ithink it will be 2x + 6y = 14y - 19x² + 12  if that's what you meant to write for that equation.. notice that the third term in the expression on the right hand side of the equation has an exponent of "2".. this would make the equation a quadratic not linear.    hope this i'm interpreting your question correctly..