Sum times difference

Statement

Expand the special product: $(5a-b)(5a+b)$

Solution

Apply the formula $(A+B)(A-B) = A^2 - B^2$ with $A=5a$ and $B=b$: $(5a-b)(5a+b) = (5a)^2 - b^2 = \boxed{25a^2 - b^2}$

Links

Topics: Literal calculus
Concepts: Special products · Sum times difference
Skills: Calculating · Using formulae
Exercise type: Evaluating expressions