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# Simplify: [(7/9)a + (9/7)b]² - ab

**Solution:**

Given, [(7/9)a + (9/7)b]² - ab

Using standard __identity__: (x+ y)² = x² + 2xy + y²

Here, x = (7/9)a and y = (9/7)b

[(7/9)a + (9/7)b]² - ab ⇒ [(7/9)a]² + 2((7/9)a) ((9/7)b) + [(9/7)b]² - ab

= (49a²/81) + 2ab + (81b²/49) - ab

= (49a²/81) + ab + (81b²/49)

**✦ Try This:** Simplify: [(4/9)p + (9/4)q]² - 2pq

Given,Simplify: [(4/9)p + (9/4)q]² - 2pq

Using standard identity: (a + b)² = a² + 2ab + b²

Here, a = (4/9)p and b = (9/4)q

=(16p²/81) + 2pq + (81q²/16) - 2pq

= (16p²/81) + (81q²/16)

**☛ Also Check: **NCERT Solutions for Class 8 Maths Chapter 9

**NCERT Exemplar Class 8 Maths Chapter 7 Problem 84(iii)**

## Simplify: [(7/9)a + (9/7)b]² - ab

**Summary:**

Simplifying [(7/9)a + (9/7)b]² - ab, we get (49a²/81) + ab + (81b²/49)

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