Quadratic Equations | Exercise 4.2

Question 4

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

Check your answer with HomiSolve it yourself, then let Homi check your steps and spot mistakes.
Solution

We will use a quadratic equation to find the two consecutive positive integers.

Step 1 — Formulate the Equation

Let's assume the first positive integer is x. The next consecutive positive integer will be x + 1. The problem states the sum of their squares is 365. So, we can write the equation.

x2+(x+1)2=365x^2 + (x+1)^2 = 365

Let's expand the term (x+1)2(x+1)^2.

x2+(x2+2x+1)=365x^2 + (x^2 + 2x + 1) = 365

Now, we combine like terms.

2x2+2x+1=3652x^2 + 2x + 1 = 365

Let's move 365 to the left side.

2x2+2x+1365=02x^2 + 2x + 1 - 365 = 0

We simplify the equation.

2x2+2x364=02x^2 + 2x - 364 = 0

We can divide the entire equation by 2.

x2+x182=0\boxed{x^2 + x - 182 = 0}

Step 2 — Solve the Equation

We need to solve this quadratic equation for x. Let's factorize the quadratic expression. We need two numbers that multiply to -182 and add up to 1. These numbers are 14 and -13.

x2+14x13x182=0x^2 + 14x - 13x - 182 = 0

Now, we factor by grouping terms.

x(x+14)13(x+14)=0x(x + 14) - 13(x + 14) = 0

We can factor out the common term (x+14)(x+14).

(x13)(x+14)=0(x - 13)(x + 14) = 0

This gives us two possible values for x. Either x13=0x - 13 = 0 or x+14=0x + 14 = 0.

x=13orx=14x = 13 \quad \text{or} \quad x = -14

The problem asks for positive integers. So, we must choose the positive value for x. Therefore, the first integer is 13. The second consecutive integer is x+1x + 1.

13+1=1413 + 1 = 14

The two consecutive positive integers are 13 and 14. Let's check our answer. 132+142=169+196=36513^2 + 14^2 = 169 + 196 = 365. This is correct.

Answer

The two consecutive positive integers are 13 and 14.

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 + \frac{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.

← Back to Quadratic Equations