ABCD is a trapezium, P and Q are mid points of the diagonals AC and BD.
If AB=17cm and CD=9cm then the length of PQ is equal to
PQ = (17-9)/2 = 4
For a proof of this, see the last exercise at
http://jwilson.coe.uga.edu/MATH7200/Sect1.3.html
To find the length of PQ, we first need to find the lengths of the diagonals AC and BD.
Since P is the midpoint of AC, we can use the information given to find the length of AC. We know that AB is 17 cm, and AD is equal to BC (as ABCD is a trapezium). To find AD (or BC), we can subtract CD from AB. So, AD = 17 cm - 9 cm = 8 cm.
Similarly, since Q is the midpoint of BD, we can find the length of BD. We know that CD is 9 cm, and CB is equal to DA (as ABCD is a trapezium). To find CB (or DA), we can subtract AB from CD. So, CB = 9 cm - 17 cm = -8 cm.
But, the length of a segment cannot be negative. So, there must be an error in the given information or the problem statement. Please check the given measurements again.