McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
3. The Quadratic Formula and the Discriminant
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Exercise 23 Page 195

Practice makes perfect
a In the Quadratic Formula, b^2-4ac is the discriminant.
ax^2+bx+c=0 ⇔ x=- b±sqrt(b^2-4ac)/2aSince the given equation is already in standard form, we can identify the values of a, b, and c. 6x^2+5x-1=0 ⇔ 6x^2+ 5x+( - 1)=0 Now, let's evaluate the discriminant.
b^2-4ac
5^2-4( 6)( - 1)
â–Ľ
Simplify
25-4(6)(- 1)
25-24(- 1)
25+24
49
The discriminant is 49.
b We want to use the discriminant of the given quadratic equation to determine the number and type of the roots. If we do not want to know the exact values of the roots, we only need to work with the discriminant. From Part A, we know that the discriminant of the given equation is 49.

Equation:& 6x^2+5x-1=0 Discriminant:& 49 Since the discriminant is greater than zero and a perfect square, the quadratic equation has two rational roots.

c We will use the Quadratic Formula to find the exact solutions of the given equation.
x=- b±sqrt(b^2-4 a c)/2 a Recall that we have already identified the values of a, b, and c in Part A, as well as the discriminant, b^2-4ac. a= 6, b= 5, c= - 1 Discriminant: 49 Let's substitute these values into the Quadratic Formula.
x=- b±sqrt(b^2-4ac)/2a
x=- 5±sqrt(49)/2( 6)
â–Ľ
Simplify
x=- 5± 7/2(6)
x=- 5± 7/12
The solutions for this equation are x= - 5± 712. Let's separate them into the positive and negative cases.
x=- 5± 7/12
x_1=- 5+7/12 x_2=- 5-7/12
x_1=2/12 x_2=- 12/12
x_1=1/6 x_2=- 1

Using the Quadratic Formula, we found that the solutions of the given equation are x_1= 16 and x_2=- 1.