Line: y-3=(12-3)/(2-1)(x-1)=9(x-1); y=9x-9+3=9x-6 (red)
Exponential: y=abˣ; 3=ab; 12=ab²; 12/3=ab²/ab=b, b=4; 3=4a or 12=16a, a=¾; y=¾(4ˣ)=3(4ˣ⁻¹) or 3(4^(x-1)) (blue)
Power: y=ax²; 3=a, 12=4a; y=3x² (green)
(a)
(b) For x>2 the exponential curve models to the highest value, the power curve coming next highest and the line coming lowest.