Use a residual plot to assess a transformed model

Let x be the explanatory variable weekly training distance (km) and y the response variable fitness test total (points). Apply the square to the response variable only. Use the full fitted coefficients below. Report signed residuals to 1 decimal places; retain unrounded values until that final step

Use weekly training distance (km) to model fitness test total (points) for the displayed cases. Apply a square transformation to the response variable only

The fitted equation is written on the transformed coordinates. Residuals are calculated on the fitted line's own response scale: signed residual on the fitness test total² (points²) scale

A signed residual is observed transformed response minus predicted transformed response at the same transformed explanatory coordinate

The residual plot is shown below. A horizontal zero line is included