Quadratic Equations | Exercise 4.2

Question 3

Find two numbers whose sum is 27 and product is 182.

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Solution
Understand the Question
  • Let one of the numbers be xx. Since their sum is 2727, the other number is 27x27 - x.
  • Their product is given as 182182, which allows us to set up a quadratic equation: x(27x)=182x(27 - x) = 182.
  • Solving this quadratic equation by factorisation gives the values of the two numbers.

Step 1 · Formulate the Quadratic Equation

Let the first number be xx. Since the sum of the two numbers is 2727, the second number is 27x27 - x.

Given their product is 182182

x(27x)=18227xx2=182x227x+182=0\begin{aligned} x(27 - x) &= 182 \\ 27x - x^2 &= 182 \\ x^2 - 27x + 182 &= 0 \end{aligned}

Step 2 · Solve by Factorisation

Find two numbers whose sum is 27-27 and product is 182182. The numbers are 13-13 and 14-14.

x213x14x+182=0x(x13)14(x13)=0(x13)(x14)=0\begin{aligned} x^2 - 13x - 14x + 182 &= 0 \\ x(x - 13) - 14(x - 13) &= 0 \\ (x - 13)(x - 14) &= 0 \end{aligned}

Step 3 · Find the Numbers

Setting each factor to zero:

x13=0    x=13x14=0    x=14\begin{aligned} x - 13 &= 0 \implies x = 13 \\ x - 14 &= 0 \implies x = 14 \end{aligned}
  • If x=13x = 13, the second number is 2713=1427 - 13 = 14.
  • If x=14x = 14, the second number is 2714=1327 - 14 = 13.
Answer

1313 and 1414

Common Mistakes
  • Sign Error in Splitting Middle Term: Selecting +13+13 and +14+14 gives a sum of +27+27, whereas the coefficient is 27-27. Both factors must be negative (13-13 and 14-14) so that their product is +182+182 and sum is 27-27.
  • Incomplete Answer: Stopping after finding x=13x = 13 or x=14x = 14 without calculating and stating both required numbers.

More questions in Exercise 4.2

Q1

Find the roots of the following quadratic equations by factorisation:

(i) x23x10=0x^2 - 3x - 10 = 0

(ii) 2x2+x6=02x^2 + x - 6 = 0

(iii) 2x2+7x+52=0\sqrt{2}x^2 + 7x + 5\sqrt{2} = 0

(iv) 2x2x+18=02x^2 - x + \dfrac{1}{8} = 0

(v) 100x220x+1=0100x^2 - 20x + 1 = 0

Q2

Solve the problems given in Example 1.

Q3

Find two numbers whose sum is 27 and product is 182.

Q4

Find two consecutive positive integers, sum of whose squares is 365.

Q5

The altitude of a right triangle is 7 cm less than its base. If the hypotenuse is 13 cm, find the other two sides.

Q6

A cottage industry produces a certain number of pottery articles in a day. It was observed on a particular day that the cost of production of each article (in rupees) was 3 more than twice the number of articles produced on that day. If the total cost of production on that day was ₹ 90, find the number of articles produced and the cost of each article.

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