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The sum of two numbers is 10 and the sum of their squares is 68. Find the product of the numbers.

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Question

The sum of two numbers is 10 and the sum of their squares is 68. Find the product of the numbers.

Sum
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Solution

Given:

  • The sum of two numbers x and y is 10, i.e., x + y = 10.
  • The sum of their squares is 68, i.e., x2 + y2 = 68.

Step-wise calculation:

1. Start from the square of the sum:

(x + y)2 = 102

(x + y)2 = 100

Expanding the left side:

x2 + y2 + 2xy = 100

2. Substitute x2 + y2 = 68:

68 + 2xy = 100

3. Solve for the product xy: 

2xy = 100 – 68

2xy = 32

xy = `32/2`

xy = 16

The product of the two numbers is 16.

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Chapter 3: Expansions - Exercise 3B [Page 73]

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Nootan Mathematics [English] Class 9 ICSE
Chapter 3 Expansions
Exercise 3B | Q 29. | Page 73
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