Algebra · JSS 2, JSS 3
Difference of two squares
Factorise one square minus another, or do quick mental sums.
- a2 − b2 = (a + b)(a − b)
What the letters mean
- a, b
- any numbers or terms
Worked example
Evaluate 512 − 492.
Step 1: Use the formula
512 − 492 = (51 + 49)(51 − 49)
Step 2: Multiply
= 100 × 2 = 200
Final answer: 200
See it
Play with this picture from the Factorisation lesson.
Each part's area = its side × its top. Dashed pink parts are negative.
Sides: (x + 3)(x + 4)
Parts: x2 + 4x + 3x + 12
Area = x2 + 7x + 12
p in (x + p)3
q in (x + q)4