If we know the total length and the length of one part of the segment, we can form an equation using the Segment Addition Postulate.
RT=25
Practice makes perfect
To find RS, we should use the Segment Addition Postulate. This postulate tells us that, if we have a point between two points, we can add the lengths of the two smaller segments to find the length of the longer segment. In our case, S is between R and T, so we can get the length RS by subtracting ST from RT.
RT = RS + ST ⇔ RS= RT - ST
We know that the length RT is 40 and the length ST is 15. Now, we can use this to calculate RS.
