Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
4. Adding and Subtracting Rational Expressions
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Exercise 59 Page 390

Find the vertex and the axis of symmetry of the parabola.

Graph:

Solutions: ( 12,- 1) and ( 94, 278)

Practice makes perfect

To solve the system of equations by graphing, we will draw the graph of the quadratic function and the linear function on the same coordinate grid. Let's start with the parabola.

Graphing the Parabola

To graph the parabola, we first need to identify a, b, and c. 2x^2-3x-y=0 ⇕ y= 2x^2+( - 3)x+ 0 For this equation we have that a= 2, b= - 3, and c= 0. Now, we can find the vertex using its formula. To do this, we will need to think of y as a function of x, y=f(x). Vertex of a Parabola: ( - b/2 a,f(- b/2 a) ) Let's find the x-coordinate of the vertex.
- b/2a
- - 3/2( 2)
- - 3/4
3/4
We use the x-coordinate of the vertex to find its y-coordinate by substituting it into the given equation.
y=2x^2-3x
y=2( 3/4)^2-3( 3/4)
â–Ľ
Simplify right-hand side
y=2(9/16)-3(3/4)
y=18/16-9/4
y=18/16-36/16
y=-18/16
y=- 9/8
The y-coordinate of the vertex is - 98. Therefore, the vertex is at the point ( 34,- 98). With this, we also know that the axis of symmetry of the parabola is the line x= 34. Next, let's find two more points on the curve, one on each side of the axis of symmetry.
x 2x^2-3x y=2x^2-3x
0 2( 0)^2-3( 0) 0
2 2( 2)^2-3( 2) 2

Both ( 0, 0) and ( 2, 2) are on the graph. Let's form the parabola by connecting these points and the vertex with a smooth curve.

Graphing the Line

Let's now graph the linear function on the same coordinate plane. We will start by rewriting the given equation in slope-intercept form.
5/2x-y=9/4
- y=9/4-5/2x
y=- 9/4+5/2x
y=5/2x-9/4
We can now identify the slope m and y-intercept b of the given function. y=5/2x-9/4 ⇔ y= 5/2x+( - 9/4) The slope of the line is 52 and the y-intercept is - 94.

Finding the Solutions

Finally, let's try to identify the coordinates of the points of intersection of the parabola and the line.

It looks like the points of intersection occur at ( 12,- 1) and (2 14, 3 38), which is equivalent to ( 94, 278).

Checking the Answer

To check our answers, we will substitute the values of the points of intersection in both equations of the system. If they produce true statements, our solution is correct. Let's start with ( 12, - 1).
2x^2-3x-y=0 & (I) 5/2x-y=9/4 & (II)

(I), (II): x= 12, y= - 1

2( 12)^2-3( 12)-( - 1)? =0 52( 12)-( - 1)? = 94
â–Ľ
Simplify left-hand side
2( 14)-3( 12)-(- 1)? =0 52( 12)-(- 1)? = 94
24- 32-(- 1)? =0 52( 12)-(- 1)? = 94
12- 32-(- 1)? =0 52( 12)-(- 1)? = 94
12- 32-(- 1)? =0 54-(- 1)? = 94

(I), (II): 1=a/a

12- 32-(- 22)? =0 54-(- 44)? = 94

(I), (II): a-(- b)=a+b

12- 32+ 22? =0 54+ 44? = 94

(I), (II): Add and subtract fractions

0=0 âś“ 94= 94 âś“
Equation (I) and Equation (II) both produced true statements. Therefore, ( 12,- 1) is a correct solution. Let's continue by checking ( 94, 278).
2x^2-3x-y=0 & (I) 5/2x-y=9/4 & (II)

(I), (II): x= 9/4, y= 27/8

2( 94)^2-3( 94)- 278? =0 52( 94)- 278? = 94
â–Ľ
Simplify left-hand side
2( 8116)-3( 94)- 278? =0 52( 94)- 278? = 94
16216- 274- 278? =0 52( 94)- 278? = 94
818- 274- 278? =0 52( 94)- 278? = 94
818- 548- 278? =0 52( 94)- 278? = 94
818- 548- 278? =0 458- 278? = 94

(I), (II): Add and subtract fractions

0=0 âś“ 188? = 94
0=0 âś“ 94= 94 âś“
Again, Equation (I) and (II) both produced true statements. Therefore, ( 94, 278) is another correct solution.