Factorise 49a2 + 70ab + 25b2.

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RRB Group D 14 Sept 2022 Shift 3 Official Paper
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  1. (7a - 5b)2
  2. (7a + 5b)2
  3. (5a - 7b)2
  4. (5a + 7b)2

Answer (Detailed Solution Below)

Option 2 : (7a + 5b)2
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Detailed Solution

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Given:  49a2 + 70ab + 25b2.

Formula used:

  • (a + b)2 = a+ 2ab + b2

Calculations:

We know that 49 = 72, 70 = 2 × 5 × 7, and 25 = 52

Now the equation becomes,

72a+ (× 5 × 7) ab + 52b2 

= (7a)2+ 2(7a) (5b) + (5b)2

As the equation represents the Property, (a+ b)2 

So, (7a)22(7a) (5b) + (5b)2

= (7a+5b)2

Therefore, the correct answer is option 2.

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