Question

The value of $(5-\sqrt{13})(5+\sqrt{13})$ is :

• A. 12
• B. 13
• C. 25
• D. 10

Answer 1

The correct option is A 12

Using the identity $(a-\sqrt{b})(a+\sqrt{b})=a^2-b$,

$(5-\sqrt{13})(5+\sqrt{13})=5^2-13=25-13=12$