Question

What is the length of DE in the right triangle below

Answer 1

The answer is B

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

\begin{lgathered}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.\end{lgathered}

DE

2

=DF

2

+EF

2

⇒DE

2

=15

2

+20

2

⇒DE

2

=225+400

⇒DE

2

=625

⇒DE

2

=25

2

⇒DE=25.