Solving the Interesting Equation: Rac{(√7 + √3)²}{(√7)² − (√3)²} = (7 + 2√21 + 3)/(7 − 3) = (5 + √21)/2

Mathematics often hides elegant truths beneath layers of symbols and operations. One such intriguing relation involves radical expressions:
rac{(√7 + √3)²}{(√7)² − (√3)²} = (5 + √21)/2

In this article, we’ll break down this identity step-by-step, clarify implicit steps, and explore why this result—combining binomial expansion, algebraic simplification, and the difference of squares—is both elegant and instructive.

Understanding the Context


Step 1: Expand the Numerator — (√7 + √3)²

The expression begins with the numerator:
(√7 + √3)²

Using the algebraic identity:
(a + b)² = a² + 2ab + b²
we expand:
(√7 + √3)² = (√7)² + 2(√7)(√3) + (√3)²

Key Insights

Calculate each term:

  • (√7)² = 7
  • (√3)² = 3
  • 2(√7)(√3) = 2√(7·3) = 2√21

Thus,
(√7 + √3)² = 7 + 2√21 + 3 = 10 + 2√21


Step 2: Simplify the Denominator — (√7)² − (√3)²

The denominator is a classic difference of squares:
(√7)² − (√3)²

Final Thoughts

Apply the identity:
a² − b² = (a − b)(a + b)
but here we can directly simplify:
(√7)² = 7, (√3)² = 3
⇒ 7 − 3 = 4

So, the denominator becomes 4.


Step 3: Combine Numerator and Denominator

Now substitute the simplified forms back into the original fraction:
rac{(√7 + √3)²}{(√7)² − (√3)²} = (10 + 2√21) / 4

Factor numerator:
= [2(5 + √21)] / 4
= (5 + √21) / 2


Why This Equality Matters

This identity demonstrates a powerful fusion of:

  • Binomial expansion for radicals
  • Difference of squares formula
  • Careful algebraic simplification