Quadratic Equations | Exercise 4.3

Question 1

Find the nature of the roots of the following quadratic equations. If the real roots exist, find them:

(i) 2x23x+5=02x^2 - 3x + 5 = 0

(ii) 3x243x+4=03x^2 - 4\sqrt{3} x + 4 = 0

(iii) 2x26x+3=02x^2 - 6x + 3 = 0

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Solution

We will use the discriminant to determine the nature of the roots.

Step 1 — Analyze Equation (i)

Let's look at the first equation. The equation is 2x23x+5=02x^2 - 3x + 5 = 0. We compare it to ax2+bx+c=0ax^2 + bx + c = 0. Here, a = 2, b = -3, and c = 5. Now, we calculate the discriminant D.

D=b24acD = b^2 - 4ac

D=(3)24×2×5D = (-3)^2 - 4 \times 2 \times 5

D=940D = 9 - 40

D=31\boxed{D = -31}

Since D < 0, the roots are not real. There are no real roots for this equation.

Step 2 — Analyze Equation (ii)

Let's look at the second equation. The equation is 3x243x+4=03x^2 - 4\sqrt{3} x + 4 = 0. We compare it to ax2+bx+c=0ax^2 + bx + c = 0. Here, a = 3, b = -4√3, and c = 4. Now, we calculate the discriminant D.

D=b24acD = b^2 - 4ac

D=(43)24×3×4D = (-4\sqrt{3})^2 - 4 \times 3 \times 4

D=(16×3)48D = (16 \times 3) - 48

D=4848D = 48 - 48

D=0\boxed{D = 0}

Since D = 0, the roots are real and equal. We use the quadratic formula to find them.

x=b±D2ax = \frac{-b \pm \sqrt{D}}{2a}

x=(43)±02×3x = \frac{-(-4\sqrt{3}) \pm \sqrt{0}}{2 \times 3}

x=436x = \frac{4\sqrt{3}}{6}

x=233x = \frac{2\sqrt{3}}{3}

Roots are 233,233\boxed{\text{Roots are } \frac{2\sqrt{3}}{3}, \frac{2\sqrt{3}}{3}}

Step 3 — Analyze Equation (iii)

Let's look at the third equation. The equation is 2x26x+3=02x^2 - 6x + 3 = 0. We compare it to ax2+bx+c=0ax^2 + bx + c = 0. Here, a = 2, b = -6, and c = 3. Now, we calculate the discriminant D.

D=b24acD = b^2 - 4ac

D=(6)24×2×3D = (-6)^2 - 4 \times 2 \times 3

D=3624D = 36 - 24

D=12\boxed{D = 12}

Since D > 0, the roots are real and distinct. We use the quadratic formula to find them.

x=b±D2ax = \frac{-b \pm \sqrt{D}}{2a}

x=(6)±122×2x = \frac{-(-6) \pm \sqrt{12}}{2 \times 2}

x=6±234x = \frac{6 \pm 2\sqrt{3}}{4}

x=2(3±3)4x = \frac{2(3 \pm \sqrt{3})}{4}

x=3±32x = \frac{3 \pm \sqrt{3}}{2}

Roots are 3+32,332\boxed{\text{Roots are } \frac{3 + \sqrt{3}}{2}, \frac{3 - \sqrt{3}}{2}}

Answer

(i) The roots are not real. (ii) The roots are real and equal: 233,233\frac{2\sqrt{3}}{3}, \frac{2\sqrt{3}}{3}. (iii) The roots are real and distinct: 3+32,332\frac{3 + \sqrt{3}}{2}, \frac{3 - \sqrt{3}}{2}.

More questions in Exercise 4.3

Q1

Find the nature of the roots of the following quadratic equations. If the real roots exist, find them:

(i) 2x23x+5=02x^2 - 3x + 5 = 0

(ii) 3x243x+4=03x^2 - 4\sqrt{3} x + 4 = 0

(iii) 2x26x+3=02x^2 - 6x + 3 = 0

Q2

Find the values of kk for each of the following quadratic equations, so that they have two equal roots.

(i) 2x2+kx+3=02x^2 + kx + 3 = 0

(ii) kx(x2)+6=0kx (x - 2) + 6 = 0

Q3

Is it possible to design a rectangular mango grove whose length is twice its breadth, and the area is 800 m2800\text{ m}^2? If so, find its length and breadth.

Q4

Is the following situation possible? If so, determine their present ages.

The sum of the ages of two friends is 2020 years. Four years ago, the product of their ages in years was 4848.

Q5

Is it possible to design a rectangular park of perimeter 80 m80\text{ m} and area 400 m2400\text{ m}^2? If so, find its length and breadth.

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