What is the length of DE in the right triangle below ?

Question

asked Jun 3, 2018 120k views

2 Answers

Jacek Dominiak · Answer 1 · 2018-06-10T10:45:55+0000

Answer: The length of DE is (B) 25 units.

Step-by-step explanation: As shown in the given figure, ΔDEF is a right-angles triangle, where ∠DFE = 90°, DF = 15 units and EF = 20 units.

We are to find the length of DE.

ΔDEF is right-angled at ∠DFE.

So, using Pythagoras theorem, we have

$DE^2=DF^2+EF^2\\\\\Rightarrow DE^2=15^2+20^2\\\\\Rightarrow DE^2=225+400\\\\\Rightarrow DE^2=625\\\\\Rightarrow DE^2=25^2\\\\\Rightarrow DE=25.$

Therefore, the length of DE is 25 units.

Thus, (B) is the correct option.