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Is 1/4 the correct answer? To the box before and how did you solve it

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Solve 7/x-4-5x+3=2/x^2-x-12
asked Nov 6, 2014 in ALGEBRA 2 by doan12345 Pupil

1 Answer

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The equation 7/(x - 4) - 5x + 3 = 2/(x2 - x - 12)

7/(x - 4) - 5x + 3 = 2/[(x  + 3)(x - 4)]

7/(x - 4) - 5x + 3 - 2/[(x  + 3)(x - 4)]  = 0

[ 7(x + 3) - 5x(x  + 3)(x - 4) + 3(x  + 3)(x - 4) - 2 ]/(x - 4)(x + 3) = 0

7x + 21 - (5x2 + 15x)(x - 4) + (3x + 9)(x - 4) - 2  = (0)(x - 4)(x + 3)

 7x + 21 - (5x3 - 20x2 + 15x2 - 60x) + (3x2 - 12x + 9x - 36 - 2) = 0

 7x + 21 - (5x3 - 5x2 - 60x) + (3x2 - 3x - 38) = 0

7x + 21 - 5x3 + 5x2 + 60x + 3x2 - 3x - 38 = 0

 - 5x3 + 8x2 + 64x - 17 = 0

Solve the above cubic polynomial using factoring.

Graph

The points where it crosses the x axis  will give solutions to the polynomial function .

The graph crosses the x - axis at a point that would suggest a factor.

It crosses the x - axis at three points hence there are 3 real roots.

 Now x  = -3.0166

Use synthetic division to determine if the given value of x is a root of the polynomial.

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Since f(-0.6503) = 0, x = -0.6503 is a zero.

The depressed polynomial is  - 5x2 + 23.083x - 5.6321

Since the depressed polynomial of this zero, - 5x2 + 23.083x - 5.6321 = 0, is quadratic,

Use the Quadratic Formula to find the roots of the related quadratic equation ax2 + bx + c = 0

a = -5, b = 23.083, c = - 5.6321

Roots are

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Solutions are x = 0.2585 , 4.3581 and -3.0661.

One of the solution is approximately x = 1/4.

answered Nov 6, 2014 by david Expert
edited Nov 6, 2014 by david

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