Algebra 1 : How to find the solution of a rational equation with a binomial denominator

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #2 : Solving Rational Expressions

Simplify:

 

\displaystyle \frac{2x-3}{3-2x}

Possible Answers:

\displaystyle 0

\displaystyle 1

\displaystyle -1

\displaystyle \frac{2}{3}

\displaystyle \frac{3}{2}

Correct answer:

\displaystyle -1

Explanation:

Factor out \displaystyle -1 from the numerator which gives us

Hence we get the following

which is equal to \displaystyle -1

Example Question #2 : How To Find The Solution Of A Rational Equation With A Binomial Denominator

Simplify:

 

\displaystyle \frac{x+3}{x^{2}+6x+9}

 

Possible Answers:

\displaystyle \frac{1}{\left ( x+3 \right )^{2}}

\displaystyle \frac{1}{x+3}

\displaystyle \left ( x+3 \right )

\displaystyle \left ( x-3 \right )

\displaystyle \left ( x+3 \right )^{2}

Correct answer:

\displaystyle \frac{1}{x+3}

Explanation:

If we factors the denominator we get

\displaystyle \left ( x+3 \right )^{2}

Hence the rational expression becomes equal to

 

\displaystyle \frac{\left ( x+3 \right )}{\left ( x+3 \right )^{2}}

 

which is equal to \displaystyle \frac{1}{\left ( x+3 \right )}

Example Question #1 : Understanding Rational Expressions

 

 

Which of the following fractions is NOT equivalent to \displaystyle - \frac{x-5}{2x + 3} ?

 

Possible Answers:

\displaystyle \frac{x+5}{2x + 3}

\displaystyle \frac{x-5}{-2x-3}

\displaystyle \frac{-x+5}{2x+3}

Correct answer:

\displaystyle \frac{x+5}{2x + 3}

Explanation:

We know that \displaystyle -\frac{a}{b} is equivalent to \displaystyle \frac{-a}{b} or \displaystyle \frac{a}{-b}.

By this property, there is no way to get \displaystyle \frac{x+5}{2x+3} from \displaystyle -\frac{x-5}{2x+3}.

Therefore the correct answer is \displaystyle \frac{x+5}{2x+3}.

Example Question #3 : Understanding Rational Expressions

Find the values of \displaystyle x which will make the given rational expression undefined:

 

\displaystyle \frac{x+5}{\left ( x-1 \right )\left ( x+2 \right )}

Possible Answers:

\displaystyle x = -5, +2

\displaystyle x = -1, -2

\displaystyle x = 1, -2

\displaystyle x = -1, 2

\displaystyle x = -5, 1

Correct answer:

\displaystyle x = 1, -2

Explanation:

If \displaystyle \left ( x-1 \right ) = 0 or \displaystyle \left ( x+2 \right ) =0, the denominator is 0, which makes the expression undefined.

 This happens when x = 1 or when x = -2.

Therefore the correct answer is \displaystyle x = 1, -2.

Example Question #4 : Solving Rational Expressions

\displaystyle \frac{y+1}{8y+2} + \frac{3}{y} = \frac{5}{3}

Solve for \displaystyle y.

 

Possible Answers:

\displaystyle y=2\displaystyle y=-\frac{9}{37}

\displaystyle y=6\displaystyle y=-\frac{7}{15}

\displaystyle y=-\frac{5}{2}

\displaystyle y=-1\displaystyle y=4

\displaystyle y=4\displaystyle y=0

Correct answer:

\displaystyle y=2\displaystyle y=-\frac{9}{37}

Explanation:

The two fractions on the left side of the equation need a common denominator. We can easily do find one by multiplying both the top and bottom of each fraction by the denominator of the other.

 \displaystyle \frac{y+1}{8y+2}\cdot \frac{y}{y}  becomes \displaystyle \frac{y^{2}+y}{(y)(8y+2)}.

\displaystyle \frac{3}{y}\cdot \frac{8y+2}{8y+2}  becomes \displaystyle \frac{24y+6}{(y)(8y+2)}.

Now add the two fractions: \displaystyle \frac{y^{2}+25y+6}{(y)(8y+2)}

To solve, multiply both sides of the equation by \displaystyle (y)(8y+2), yielding

 \displaystyle y^{2}+25y+6 = \frac{(40y^{2}+10y)}{3}.

Multiply both sides by 3:

 \displaystyle 3y^{2}+75y+18 = 40y^{2}+ 10y

Move all terms to the same side:

 \displaystyle 37y^{2}-65y-18 = 0

This looks like a complicated equation to factor, but luckily, the only factors of 37 are 37 and 1, so we are left with

 \displaystyle (37y+9)(y-2).

Our solutions are therefore

\displaystyle y=2 

and

\displaystyle y=-\frac{9}{37}.

Example Question #1 : How To Find The Solution Of A Rational Equation With A Binomial Denominator

Simplify the expression:

\displaystyle \frac{x^{3}-5x^{2}+6x}{x-3}

Possible Answers:

\displaystyle x-2

\displaystyle x^{2}-2x

\displaystyle \frac{x}{x-3}

\displaystyle x^{2}-3x

\displaystyle x^{2}-5x-3

Correct answer:

\displaystyle x^{2}-2x

Explanation:

First, factor out x from the numerator:

\displaystyle \frac{x^{3}-5x^{2}+6x}{x-3}\displaystyle =\frac{x(x^{2}-5x+6)}{x-3}

Notice that the resultant expression in the parentheses is quadratic. This expression can be further factored:

\displaystyle =\frac{x(x-2)(x-3)}{x-3}

We can then cancel the (x-3) which appears in both the numerator and denominator:

\displaystyle =\frac{x(x-2)}{1}

Finally, distribute the x outside of the parentheses to reach our answer:

\displaystyle =x^{2}-2x

Example Question #1 : How To Find The Solution Of A Rational Equation With A Binomial Denominator

Solve for \displaystyle y.

\displaystyle 2=\frac{10}{3y+2x^{2}}

Possible Answers:

\displaystyle y=\frac{3}{5}+\frac{3}{2}x^{2}

\displaystyle y=10+4x^{2}

None of the other answers.

\displaystyle y=\frac{4}{6}x^{2}-10

Correct answer:

\displaystyle y=\frac{3}{5}+\frac{3}{2}x^{2}

Explanation:

Multiply each side by \displaystyle 3y+2x^{2}

\displaystyle 2(3y+2x^{2})=10

Distribute 2 to each term of the polynomial.

\displaystyle 6y+4x^{2}=10

Divide the polynomial by 6.

\displaystyle 6(y+\frac{2}{3}x^{2})=10

Divide each side by 6.

\displaystyle y+\frac{2}{3}x^{2}=\frac{5}{3}

Subtract the \displaystyle x term from each side.

\displaystyle y=\frac{5}{3}-\frac{2}{3}x^{2}

Example Question #8 : How To Find The Solution Of A Rational Equation With A Binomial Denominator

Solve for \displaystyle k.

\displaystyle 3=\frac{10}{k+2}

Possible Answers:

\displaystyle \frac{3}{4}

\displaystyle \frac{8}{3}

\displaystyle \frac{-4}{3}

\displaystyle 10

\displaystyle \frac{4}{3}

Correct answer:

\displaystyle \frac{4}{3}

Explanation:

Multiply each side by \displaystyle (k+2)

\displaystyle 3(k+2)=10

Distribute 3 to the terms in parentheses.

\displaystyle 3k+6=10

Subtract 6 from each side of the equation.

\displaystyle 3k=4

Divide each side by 3.

\displaystyle k=\frac{4}{3}

Example Question #2 : How To Find The Solution Of A Rational Equation With A Binomial Denominator

Solve for \displaystyle n.

\displaystyle 5=\frac{105}{n^{2}+5}

Possible Answers:

\displaystyle \sqrt{19}

\displaystyle 16

\displaystyle \sqrt{80}

\displaystyle -16

\displaystyle 4

Correct answer:

\displaystyle 4

Explanation:

\displaystyle 5=\frac{105}{n^{2}+5}

Multiply each side of the equation by \displaystyle n^{2}+5

\displaystyle 5(n^{2}+5)=105

Distribute 5 to each term in parentheses.

\displaystyle 5n^{2}+25=105

Subtract 25 from each side of equation.

\displaystyle 5n^{2}=80

Divide each side of equation by 5.

\displaystyle n^{2}=16

Square root of each side of equation.

\displaystyle n=4

Example Question #1 : Multiplying And Dividing Rational Expressions

\displaystyle \small \frac{x^2-5x-6}{x+1}

For all values \displaystyle x\neq -1, which of the following is equivalent to the expression above?

Possible Answers:

\displaystyle \small x+6

\displaystyle \small x-3

\displaystyle \small x-6

\displaystyle \small x-2

Correct answer:

\displaystyle \small x-6

Explanation:

First, factor the numerator. We need factors that multiply to \displaystyle \small -6 and add to \displaystyle \small -5.

\displaystyle \small 1*-6=-6\ \text{and}\ 1+(-6)=-5

\displaystyle \small x^2-5x-6=(x-6)(x+1)

We can plug the factored terms into the original expression.

\displaystyle \small \frac{x^2-5x-6}{x+1}=\frac{(x-6)(x+1)}{(x+1)}

Note that \displaystyle \small (x+1) appears in both the numerator and the denominator. This allows us to cancel the terms.

\displaystyle \frac{(x-6)(x+1)}{(x+1)}=(x-6)

This is our final answer.

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