Quadratic Equations | Exercise 4.1

Question 2

  1. Represent the following situations in the form of quadratic equations :

(i) The area of a rectangular plot is 528 m2528\text{ m}^2. The length of the plot (in metres) is one more than twice its breadth. We need to find the length and breadth of the plot.

(ii) The product of two consecutive positive integers is 306. We need to find the integers.

(iii) Rohan's mother is 26 years older than him. The product of their ages (in years) 3 years from now will be 360. We would like to find Rohan's present age.

(iv) A train travels a distance of 480 km at a uniform speed. If the speed had been 8 km/h less, then it would have taken 3 hours more to cover the same distance. We need to find the speed of the train.

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Solution

Let's represent each situation as a quadratic equation.

Step 1 — Rectangular Plot Dimensions

We need to find the length and breadth of the plot. Let the breadth of the rectangular plot be xx metres. The length is one more than twice its breadth. So, the length is (2x+1)(2x + 1) metres. The area of the plot is given as 528 m2528 \text{ m}^2. The area of a rectangle is length multiplied by breadth.

x(2x+1)=528x(2x + 1) = 528

Let's expand the left side.

2x2+x=5282x^2 + x = 528

Now, we move all terms to one side to form a quadratic equation.

2x2+x528=02x^2 + x - 528 = 0

2x2+x528=0\boxed{2x^2 + x - 528 = 0}

This equation represents the situation for the rectangular plot.

Step 2 — Consecutive Integers Product

We need to find two consecutive positive integers. Let the first positive integer be xx. Since they are consecutive, the next integer will be x+1x + 1. Their product is given as 306.

x(x+1)=306x(x + 1) = 306

Let's expand the left side of the equation.

x2+x=306x^2 + x = 306

Now, we move 306 to the left side to get the standard quadratic form.

x2+x306=0x^2 + x - 306 = 0

x2+x306=0\boxed{x^2 + x - 306 = 0}

This equation represents the situation for the consecutive integers.

Step 3 — Rohan's Age

We need to find Rohan's present age. Let Rohan's present age be xx years. Rohan's mother is 26 years older than him. So, his mother's present age is (x+26)(x + 26) years. We consider their ages 3 years from now. Rohan's age after 3 years will be (x+3)(x + 3) years. His mother's age after 3 years will be (x+26+3)(x + 26 + 3), which is (x+29)(x + 29) years. The product of their ages 3 years from now will be 360.

(x+3)(x+29)=360(x + 3)(x + 29) = 360

Let's expand the left side using the distributive property.

x2+29x+3x+87=360x^2 + 29x + 3x + 87 = 360

Combine the like terms.

x2+32x+87=360x^2 + 32x + 87 = 360

Now, we move 360 to the left side to form the quadratic equation.

x2+32x+87360=0x^2 + 32x + 87 - 360 = 0

x2+32x273=0x^2 + 32x - 273 = 0

x2+32x273=0\boxed{x^2 + 32x - 273 = 0}

This equation represents the situation for Rohan's age.

Step 4 — Train Speed

We need to find the speed of the train. Let the uniform speed of the train be x km/hx \text{ km/h}. The distance traveled is 480 km. The time taken to cover this distance is DistanceSpeed\frac{\text{Distance}}{\text{Speed}}.

Time=480x hours\text{Time} = \frac{480}{x} \text{ hours}

If the speed had been 8 km/h less, the new speed would be (x8) km/h(x - 8) \text{ km/h}. The new time taken would be 480x8 hours\frac{480}{x - 8} \text{ hours}. This new time is 3 hours more than the original time.

480x8=480x+3\frac{480}{x - 8} = \frac{480}{x} + 3

Let's rearrange the equation to isolate the terms with xx.

480x8480x=3\frac{480}{x - 8} - \frac{480}{x} = 3

Now, we find a common denominator for the left side.

480x480(x8)x(x8)=3\frac{480x - 480(x - 8)}{x(x - 8)} = 3

Let's expand the numerator and the denominator.

480x480x+3840x28x=3\frac{480x - 480x + 3840}{x^2 - 8x} = 3

Simplify the numerator.

3840x28x=3\frac{3840}{x^2 - 8x} = 3

Multiply both sides by (x28x)(x^2 - 8x).

3840=3(x28x)3840 = 3(x^2 - 8x)

3840=3x224x3840 = 3x^2 - 24x

Finally, move all terms to one side to form the quadratic equation.

0=3x224x38400 = 3x^2 - 24x - 3840

3x224x3840=03x^2 - 24x - 3840 = 0

3x224x3840=0\boxed{3x^2 - 24x - 3840 = 0}

This equation represents the situation for the train's speed.

Answer

(i) The length and breadth of the plot satisfy the equation 2x2+x528=02x^2 + x - 528 = 0. (ii) The two consecutive positive integers satisfy the quadratic equation x2+x306=0x^2 + x - 306 = 0. (iii) Rohan's present age satisfies the quadratic equation x2+32x273=0x^2 + 32x - 273 = 0. (iv) The speed of the train satisfies the quadratic equation 3x224x3840=03x^2 - 24x - 3840 = 0.

More questions in Exercise 4.1

Q1
  1. Check whether the following are quadratic equations :

(i) (x+1)2=2(x3)(x + 1)^2 = 2(x - 3)

(ii) x22x=(2)(3x)x^2 - 2x = (-2) (3 - x)

(iii) (x2)(x+1)=(x1)(x+3)(x - 2)(x + 1) = (x - 1)(x + 3)

(iv) (x3)(2x+1)=x(x+5)(x - 3)(2x + 1) = x(x + 5)

(v) (2x1)(x3)=(x+5)(x1)(2x - 1)(x - 3) = (x + 5)(x - 1)

(vi) x2+3x+1=(x2)2x^2 + 3x + 1 = (x - 2)^2

(vii) (x+2)3=2x(x21)(x + 2)^3 = 2x(x^2 - 1)

(viii) x34x2x+1=(x2)3x^3 - 4x^2 - x + 1 = (x - 2)^3

Q2
  1. Represent the following situations in the form of quadratic equations :

(i) The area of a rectangular plot is 528 m2528\text{ m}^2. The length of the plot (in metres) is one more than twice its breadth. We need to find the length and breadth of the plot.

(ii) The product of two consecutive positive integers is 306. We need to find the integers.

(iii) Rohan's mother is 26 years older than him. The product of their ages (in years) 3 years from now will be 360. We would like to find Rohan's present age.

(iv) A train travels a distance of 480 km at a uniform speed. If the speed had been 8 km/h less, then it would have taken 3 hours more to cover the same distance. We need to find the speed of the train.

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