In ∆ DEF, ∠ E = 900 , If DE = 4 cm, EF = 3 cm, What is the length of side DF?

Solution:

In ∆ DEF, ∠ E = 900  [Given]

∴ DF2 = DE2 + EF2   [By Pythagoras theorem]

∴ DF2 = 42 + 32

∴ DF2 = 16 + 9

∴ DF2 = 25

∴ DF = √25

∴ DF = 5 cm

Ans. The length of DF is 5 cm.