Attempt the question, check the explanation, and continue with similar questions to build confidence before exams.
D = sqrt((x2 - x1) + (y2 - y1) + (z2 - z1))
D = (x2 - x1) + (y2 - y1) + (z2 - z1)
D = sqrt((x2 - x1)^2 + (y2 - y1)^2 + (z2 - z1)^2)
D = (x2 - x1)^2 + (y2 - y1)^2 + (z2 - z1)^2
Continue with nearby questions to strengthen the same chapter concept while you still have the context fresh in mind.