+1639 Find the length of the common internal tangent PQ. (See diagram)
+1694 There are a couple of similar right triangles: APC and BQC
AB = 5 AP = 1 AC = x BQ = 3 BC = 5 - x
AP / AC = BQ / BC
1 / x = 3 / (5 - x)
4x = 5
x = 1.25
AC = 1.25 BC = 3.75
PC = sqrt(AC2 - AP2) = 0.75
QC = (PC * BQ) / AP QC = 2.25
PQ = PC + QC
PQ = 3 cm
