DEF is a right angle ?

False

Step-by-step explanation:

Since we want to test if it is a right triangle, we can use Pythagorean Theorem

a^2+b^2=c^2

where a and b are the legs, and c is the hypotenuse.

In the given triangle, 23 and 26 are the legs, since they are shorter sides.  42 is the hypotenuse, since it is the longest side.

Therefore, a is 23, b is 26 and c is 42. Substitute these values into the equation

23^2+26^2=42^2

Evaluate the exponents

529+676=1764

Add 529 and 676

1205=1764

This statement is not true, 1205 is not equal to 1764. Therefore this is not a right triangle.