McGraw Hill Glencoe Algebra 2, 2012
MH
McGraw Hill Glencoe Algebra 2, 2012 View details
6. Solving Rational Equations and Inequalities
Continue to next subchapter

Exercise 20 Page 577

Factor the denominators, and multiply both sides of the equation by the least common denominator (LCD).

x=- 12 and x=2

Practice makes perfect

We want to solve the given rational equation. x/2x-1+3/x+4=21/2x^2+7x-4 We will start by factoring the denominators to find the least common denominator (LCD). Note that the first and second denominators are already factored. Let's factor the third one.

2x^2+7x-4
2x^2+8x-x-4
â–¼
Factor out 2x & - 1
2x(x+4)-x-4
2x(x+4)-1(x+4)
(x+4)(2x-1)
We can now rewrite the given expression. x/2x-1+3/x+4=21/2x^2+7x-4 ⇕ x/2x-1+3/x+4=21/(x+4) (2x-1) We will solve the equation by multiplying each side by the LCD to clear denominators.

x/2x-1+3/x+4=21/(x+4)(2x-1)
( x/2x-1+3/x+4) * (x+4) (2x-1)=21/(x+4)(2x-1)* (x+4) (2x-1)
x(x+4)(2x-1)/2x-1+3(x+4)(2x-1)/x+4=21(x+4)(2x-1)/(x+4)(2x-1)
x(x+4)(2x-1)/2x-1+3(x+4)(2x-1)/x+4=21(x+4)(2x-1)/(x+4)(2x-1)
x(x+4)+3(2x-1)=21
â–¼
Simplify
x^2+4x+3(2x-1)=21
x^2+4x+6x-3=21
x^2+10x-3=21
x^2+10x-24=0

Note that we have a quadratic equation now. Let's identify the values of a, b, and c. x^2+10x-24=0 ⇕ 1x^2 +10x+(- 24)=0 We have that a= 1, b=10, and c=-24. Let's substitute these values into the Quadratic Formula and solve for x.

x=- b±sqrt(b^2-4ac)/2a
x=- 10±sqrt(10^2-4( 1)(-24))/2( 1)
â–¼
Simplify right-hand side
x=- 10±sqrt(100+96)/2
x=- 10±sqrt(196)/2
x=- 10± 14/2

Let's calculate both solutions by using the positive and negative signs.

x=- 10± 14/2
x=- 10+ 14/2 x=- 10- 14/2
x=4/2 x=- 24/2
x=2 x=-12

Finally, we will check if either x=2 or x=-12 is an extraneous solution. To do this, we need to substitute 2 and - 12 for x in the original equation. Let's start with x=2.

x/2x-1+3/x+4=21/2x^2+7x-4
2/2( 2)-1+3/2+4? =21/2( 2^2)+7( 2)-4
â–¼
Simplify
2/4-1+3/2+4? =21/8+14-4
2/3+3/6? =21/18
2/3+3/6? =7/6
2*2/3*2+3/6? =7/6
4/6+3/6? =7/6
7/6=7/6 ✓



Now, we will check our second solution, x=-12.

x/2x-1+3/x+4=21/2x^2+7x-4
-12/2( -12)-1+3/-12+4? =21/2( -12)^2+7( -12)-4
â–¼
Simplify
-12/-24-1+3/-12+4? =21/288-84-4
-12/-25+3/-8? =21/200
-12/-25-3/8? =21/200
12/25-3/8? =21/200
12*8/25*8-3/8? =21/200
12*8/25*8-3*25/8*25? =21/200
96/200-75/200? =21/200
21/200 = 21/200 ✓

Neither of our solutions is an extraneous solution. Therefore, the solutions to the given equation are x=2 and x=-12.