What does it mean when the coefficient a in a quadratic regression model is zero?

If a=0 that means the parable cuts y-axis in the point (0,0). Or you can say the parable passes through by the point (0,0)

I'll do the first one for you. it isn't very hard at all.on number one, you have (50 × 3), which equals 150, and (3 × 3), which equals 9. after you establish that, you add 150 and 9 together. so, (150 + 9) equals 159.this means that 53 × 3 = 159.