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Bunuel
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Bunuel

Tough and Tricky questions: Algebra.



(16x^4 – 81y^4)/(2x + 3y) = 12x^2 + 27y^2 and 4x + 3y = 9, what is x?

A. 1
B. 1.5
C. 2
D. 3
E. 4

Kudos for a correct solution.

It's important to work neatly here.

(16x^4-81y^4)/(2x+3y) = 12x^2 + 27y^2

(4x^2+9y^2)(4x^2-9y^2)/(2x+3y) = 12x^2 + 27y^2

(2x+3y)(2x-3y)(4x^2+9y^2)/(2x+3y) = 12x^2 + 27y^2

(2x-3y)(4x^2+9y^2) = 12x^2 + 27y^2

(2x-3y)(4x^2+9y^2) = 3(4x^2 + 9y^2)

2x-3y = 3
+4x+3y = 9

6x = 12
x = 2
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Hello ,
(16x^4–81y^4)/(2x+3y)=12x^2+27y^2

so this can be written as
(2x)^4-(3y)^4/(2x+3y)=12x^2+27y^2

(2x-3y)(2x+3y)(4x^2+9y^2)/2x+3y =12x^2+27y^2

solving this we get
2x-3y=3
we have 4x+3y=9

when we solve we get x=2
Hence option C is correct

Thanks
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We can simplify

(16x^4 - 81y^4) = (2x - 3y)*(2x + 3y)*(4x^2 + 9y^2)

So, we can cancel

(2x + 3y) from denominator and
(4x^2 + 9y^2) from right hand side.

Final equation
2x - 3y = 3
4x + 3y = 9.

So, x=2
Option c is correct ans
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