when Convexity = (V+ + V- - 2V0) / ( 2 * V0 * (Chainge in Yield)^2) then Change in bond price = -(Duration)(Change in Yield) + (Convexity)(Change in Yield)^2
but when Convexity = (V+ + V- - 2V0) / (V0 * (Chainge in Yield)^2) then Change in bond price = -(Duration)(Change in Yield) + 0.5 * (Convexity)(Change in Yield)^2
It was mentioned in Level 1. Try to check the reading on the measurement of interest risk.
It’s more common to include the ½ in the calculation of convexity, so you don’t include it in the formula for the price change. But it’s not universal.
Unfortunately, at Level I they have examples of each in the curriculum; including the ½ in the formula appears in the reading on credit analysis.