JAMB Mathematics 2021 Paper

Concept:The diagonals of a rhombus bisect each other at right angles, forming four right-angled triangles.Explanation:The diagonals are $6\text{ cm}$ and $8\text{ cm}$.Each diagonal is cut into two equal halves.So one half of the $6\text{ cm}$ diagonal is $3\text{ cm}$.One half of the $8\text{ cm}$ diagonal is $4\text{ cm}$.These halves are the two shorter sides of a right-angled triangle.The side of the rhombus is the hypotenuse of that triangle.Using Pythagoras theorem:$$\text{side}^2 = 3^2 + 4^2$$$$\text{side}^2 = 9 + 16 = 25$$$$\text{side} = \sqrt{25} = 5\text{ cm}$$All sides of a rhombus are equal, so the required length is $5\text{ cm}$.Answer:B. $5\text{ cm}$