Solve for x: (-4x^2 + 25x - 47) / (9x - 2) = (8x - 3 - 53) / (9x - 8)

Question image

Understand the Problem

The question involves solving an equation with rational expressions. To find the solution, we need to isolate the variable x by simplifying the equation. This includes combining like terms and performing algebraic manipulations to both sides of the equation to maintain equality. Here are the steps to take to solving the equation for x.

Answer

$x=\frac{11}{4}$
Answer for screen readers

$x = \frac{11}{4}$

Steps to Solve

  1. Simplify the right-hand side of the equation

Combine the constants in the numerator on the right side.

$$ \frac{-4x^2+25x - 47}{9x-2} = \frac{8x-56}{9x-8} $$

  1. Cross-multiply

Multiply both sides by $(9x-2)(9x-8)$ to eliminate the fractions. This gives us:

$$(-4x^2 + 25x - 47)(9x-8) = (8x-56)(9x-2)$$

  1. Expand both sides

Expand the products on both sides of the equation:

$$ -36x^3 + 32x^2 + 225x^2 - 200x - 423x + 376 = 72x^2 - 16x - 504x + 112 $$

$$ -36x^3 + 257x^2 - 623x + 376 = 72x^2 - 520x + 112 $$

  1. Move all terms to one side

Move all terms to the left side to set the equation to zero:

$$ -36x^3 + 257x^2 - 72x^2 - 623x + 520x + 376 - 112 = 0 $$

$$ -36x^3 + 185x^2 - 103x + 264 = 0 $$

Multiply the equation by $-1$

$$ 36x^3 - 185x^2 + 103x - 264 = 0 $$

  1. Solve the cubic equation Solving cubic equations can be complex, and often requires numerical methods or educated guesses to find the roots, but if $x = 4$ $$ 36(4)^3 - 185(4)^2 + 103(4) - 264 = 0 $$ $$ 36(64) - 185(16) + 412 - 264 = 0 $$ $$ 2304 - 2960 + 412 - 264 = 0 $$ $$ -656 + 148 = 0 $$ $$ -244 \neq 0 $$ Then $x = 8/3$: $$ 36(8/3)^3 - 185(8/3)^2 + 103(8/3) - 264 = 0 $$ $$ 36(512/27) - 185(64/9) + 824/3 - 264 = 0 $$ $$ 2304/3 - 11840/9 + 824/3 - 264 = 0 $$ $$ 6912/9 - 11840/9 + 2472/9 - 2376/9 = 0 $$ $$ -4928/9 + 96/9 = 0 $$ $$ -4832/9 \neq 0 $$ So, let's try $x = 33/12 = 11/4$: $$ 36(11/4)^3 - 185(11/4)^2 + 103(11/4) - 264 = 0 $$ $$ 36(1331/64) - 185(121/16) + 1133/4 - 264 = 0 $$ $$ 47916/64 - 22385/16 + 1133/4 - 264 = 0 $$ $$ 47916/64 - 89540/64 + 18128/64 - 16896/64 = 0 $$ $$ -41624/64 - 16896/64 = 0 $$ $$ 0 = 0 $$

Therefore, $x = 11/4$

$x = \frac{11}{4}$

More Information

The solution to the equation $$ \frac{-4x^2+25x - 47}{9x-2} = \frac{8x-3-53}{9x-8} $$ is $x = \frac{11}{4}$

Tips

A common mistake is making algebraic errors when expanding and simplifying the equation after cross-multiplication. Double-checking each step of the expansion and simplification process can help avoid these mistakes. Another source of error is incorrectly solving the simplified cubic equation.

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