If a, b and c are the sides of a right-angled triangle, where a > b > c, then what is the value of the expression (a + b + c) (a + b - c) (a - b + c) (a - b - c)?

A triangle has side lengths x cm, x + 31 cm and x + 26 cm. If its area is 126 square cm, then what is the value of x ?

If all the sides of a parallelogram are equal and one angle is a right angle, then it is called as

The sides of a triangle are 5 cm, 12 cm and 13 cm. then its area is

If the sides of a triangle are doubled, then its area

ABC is a triangle with sides AB = 41 cm, BC = 28 cm and CA = 15 cm. If D, E and F are the mid-points of AB, BC and CA respectively, then what is the area of the triangle DEF?