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​Simplify8x3+27y3−64z3+72xyz4x2+9y2+16z2−6xy+12yz+8zx\text{Simplify} \\\frac{8x^3 + 27y^3 - 64z^3 + 72xyz}{4x^2 + 9y^2 + 16z^2 - 6xy + 12yz + 8zx}Simp
Question

Simplify8x3+27y364z3+72xyz4x2+9y2+16z26xy+12yz+8zx\text{Simplify} \\\frac{8x^3 + 27y^3 - 64z^3 + 72xyz}{4x^2 + 9y^2 + 16z^2 - 6xy + 12yz + 8zx}​​

A.

(2x - 3x + 4z)

B.

(2x + 3y - 4z)

C.

(2x + 3y + 4z)

D.

(2x - 3y - 4z)

Correct option is B

Given:

8x3+27y364z3+72xyz4x2+9y2+16z26xy+12yz+8zx\frac{8x^{3}+27y^{3}-64z^{3}+72xyz}{4x^{2}+9y^{2}+16z^{2}-6xy+12yz+8zx}​​

Formula Used:

Identity:
a3+b3+c33abc=(a+b+c)(a2+b2+c2abbcca)a^{3}+b^{3}+c^{3}-3abc=(a+b+c)\big(a^{2}+b^{2}+c^{2}-ab-bc-ca\big)​​
Solution:

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

Numerator:
a3+b3+c33abca^{3}+b^{3}+c^{3}-3abc​​
=8x3+27y364z3+72xyz.=8x^{3}+27y^{3}-64z^{3}+72xyz. ​​

Denominator:
a2+b2+c2abbccaa^{2}+b^{2}+c^{2}-ab-bc-ca​​
=4x2+9y2+16z26xy+12yz+8zx.=4x^{2}+9y^{2}+16z^{2}-6xy+12yz+8zx.​​
Hence the expression becomes

(a+b+c)(a2+b2+c2abbcca)a2+b2+c2abbcca\frac{(a+b+c)\big(a^{2}+b^{2}+c^{2}-ab-bc-ca\big)}{a^{2}+b^{2}+c^{2}-ab-bc-ca}​​

= a + b + c

=2x + 3y - 4z.

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