Explanation:

★ Answer :

→ Method 1 :

As, we have to factorise the (3a + 5b)² - 4c²

We know that,

(a + b)² = a² + b² + 2ab

→ (3a)² + (5b)² + 2(3a)(5b) - 4c²

→ 9a² + 25b² - 4c² + 30ab

\rule{200}{2}

→ Method 2 :

→ (3a + 5b)² - 4c²

We can write 4c² as (2c)².

→ (3a + 5b)² - (2c)²

We know that,

a² - b² = (a + b)(a - b)

→ (3a + 5b - 2c)(3a + 5b + 2c)

→ 9a² + 15ab - 6ac + 15ab + 25b² - 10bc + 6ac + 10bc - 4c²

→ 9a² + 25b² - 4c² + 30ab

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