Simplify  \(\frac{8x^3 + 27y^3 - 64z^3 + 72xyz}{4x^2 + 9y^2 + 16z^2 - 6xy + 12yz + 8zx}\)

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RRB NTPC Graduate Level CBT-I Official Paper (Held On: 06 Jun, 2025 Shift 3)
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  1. (2x + 3y - 4z)
  2. (2x - 3y - 4z)
  3. (2x - 3y + 4z)
  4. (2x + 3y + 4z)

Answer (Detailed Solution Below)

Option 1 : (2x + 3y - 4z)
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Detailed Solution

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Given:

Simplify \(\frac{8x^3 + 27y^3 - 64z^3 + 72xyz}{4x^2 + 9y^2 + 16z^2 - 6xy + 12yz + 8zx}\)

Formula used:

(a3 + b3 + c3 - 3abc)/(a2 + b2 + c2 - ab - bc - ca) = (a + b + c)

Where, a = 2x, b = 3y, c = -4z

Calculation:

Numerator = 8x3 + 27y3 - 64z3 + 72xyz

⇒ Numerator = (2x)3 + (3y)3 + (-4z)3 - 3(2x)(3y)(-4z)

⇒ Numerator = a3 + b3 + c3 - 3abc

Denominator = 4x2 + 9y2 + 16z2 - 6xy + 12yz + 8zx

⇒ Denominator = (2x)2 + (3y)2 + (-4z)2 - (2x)(3y) - (3y)(-4z) - (-4z)(2x)

⇒ Denominator = a2 + b2 + c2 - ab - bc - ca

⇒ Expression = (a + b + c)

⇒ Expression = (2x + 3y - 4z)

∴ The correct answer is option (1).

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