The lengths of the sides of a triangle are 3,4,5. Can the triangle be a right triangle?

Yes.

Step-by-step explanation:

Yes, because the sides satisfy the Pythagoras theorem:

5^2 = 3^2 + 4^2

25 = 9 + 16

25 = 25.

Only a right triangle has this property.

We can use the Pythagorean theorem to test this.

a^2+b^2=c^2

If 3^2+4^2 is equal to 5^2 then it can be right angled.

3^2+4^2 = 25

5^2 = 25

Therefore it can be a right angled triangle.

Tip:

Learn a couple common Pythagorean triples to answer via inspection. These are 3 numbers that are always in a right angled triangle. If you know two of them, you'll know the third.

3; 4; 5

6; 8; 10

5; 12; 13

9; 12; 15