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Math

Math Snap

PROBLEM

Question 6
(a) Form a quadratic equation whose roots are 3123 \frac{1}{2} and 213-2 \frac{1}{3}. Express your answer in the form ax2+bx+c=0a x^{2}+b x+c=0, where a,b,ca, b, c are integers.
(b) Form an equation whose roots are twice those in previous part.

STEP 1

1. The roots of the quadratic equation are given as mixed numbers.
2. The standard form of a quadratic equation is ax2+bx+c=0 ax^2 + bx + c = 0 .
3. To form a quadratic equation from its roots, use the relationship between roots and coefficients.

STEP 2

1. Convert the given roots into improper fractions.
2. Use the sum and product of roots to form the quadratic equation.
3. Form a new equation with roots that are twice the original roots.

STEP 3

Convert the mixed numbers to improper fractions. The roots given are 312 3 \frac{1}{2} and 213 -2 \frac{1}{3} .
312=72 3 \frac{1}{2} = \frac{7}{2} 213=73 -2 \frac{1}{3} = -\frac{7}{3}

STEP 4

Use the sum and product of the roots to form the quadratic equation. If the roots are r1 r_1 and r2 r_2 , then the quadratic equation is:
x2(r1+r2)x+r1r2=0 x^2 - (r_1 + r_2)x + r_1r_2 = 0 Calculate the sum and product of the roots:
Sum:
r1+r2=72+(73)=216146=76 r_1 + r_2 = \frac{7}{2} + \left(-\frac{7}{3}\right) = \frac{21}{6} - \frac{14}{6} = \frac{7}{6} Product:
r1r2=72(73)=496 r_1 \cdot r_2 = \frac{7}{2} \cdot \left(-\frac{7}{3}\right) = -\frac{49}{6}

STEP 5

Substitute the sum and product into the quadratic equation formula:
x2(76)x496=0 x^2 - \left(\frac{7}{6}\right)x - \frac{49}{6} = 0 Multiply through by 6 to clear the fractions:
6x27x49=0 6x^2 - 7x - 49 = 0

STEP 6

Form an equation whose roots are twice those in the previous part. If the original roots are r1 r_1 and r2 r_2 , the new roots are 2r1 2r_1 and 2r2 2r_2 .
Calculate the new sum and product:
New Sum:
2r1+2r2=2(r1+r2)=2×76=73 2r_1 + 2r_2 = 2(r_1 + r_2) = 2 \times \frac{7}{6} = \frac{7}{3} New Product:
(2r1)(2r2)=4(r1r2)=4×(496)=1966=983 (2r_1)(2r_2) = 4(r_1r_2) = 4 \times \left(-\frac{49}{6}\right) = -\frac{196}{6} = -\frac{98}{3}

SOLUTION

Substitute the new sum and product into the quadratic equation formula:
x2(73)x983=0 x^2 - \left(\frac{7}{3}\right)x - \frac{98}{3} = 0 Multiply through by 3 to clear the fractions:
3x27x98=0 3x^2 - 7x - 98 = 0 The quadratic equations are:
(a) 6x27x49=0 6x^2 - 7x - 49 = 0
(b) 3x27x98=0 3x^2 - 7x - 98 = 0

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