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Operations with Integers - Multiplication of Integers

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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To multiply two integers with the same sign, multiply their absolute values and place a positive sign (++) before the product. Example: (+a)×(+b)=ab(+a) \times (+b) = ab and (−a)×(−b)=ab(-a) \times (-b) = ab.

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To multiply two integers with unlike signs, multiply their absolute values and place a negative sign (−-) before the product. Example: (+a)×(−b)=−ab(+a) \times (-b) = -ab and (−a)×(+b)=−ab(-a) \times (+b) = -ab.

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The product of an even number of negative integers is positive. For example, (−a)×(−b)×(−c)×(−d)=abcd(-a) \times (-b) \times (-c) \times (-d) = abcd.

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The product of an odd number of negative integers is negative. For example, (−a)×(−b)×(−c)=−abc(-a) \times (-b) \times (-c) = -abc.

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Commutative Property: Multiplication is commutative for integers, meaning a×b=b×aa \times b = b \times a for any integers aa and bb.

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Associative Property: For any three integers a,b,a, b, and cc, the grouping of factors does not change the product: (a×b)×c=a×(b×c)(a \times b) \times c = a \times (b \times c).

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Distributive Property: Multiplication distributes over addition and subtraction: a×(b+c)=(a×b)+(a×c)a \times (b + c) = (a \times b) + (a \times c) and a×(b−c)=(a×b)−(a×c)a \times (b - c) = (a \times b) - (a \times c).

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Multiplicative Identity: The integer 11 is the identity for multiplication. For any integer aa, a×1=1×a=aa \times 1 = 1 \times a = a.

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Multiplication by Zero: Any integer aa multiplied by zero results in zero: a×0=0×a=0a \times 0 = 0 \times a = 0.

📐Formulae

a×b=b×aa \times b = b \times a

(a×b)×c=a×(b×c)(a \times b) \times c = a \times (b \times c) tube

a×(b+c)=a×b+a×ca \times (b + c) = a \times b + a \times c

a×1=aa \times 1 = a

a×0=0a \times 0 = 0

(−1)×(−1)×... (n times)=1, if n is even(-1) \times (-1) \times ... \text{ (n times)} = 1, \text{ if } n \text{ is even}

(−1)×(−1)×... (n times)=−1, if n is odd(-1) \times (-1) \times ... \text{ (n times)} = -1, \text{ if } n \text{ is odd}

💡Examples

Problem 1:

Find the product of (−12)×(−5)×(−2)(-12) \times (-5) \times (-2).

Solution:

(−12)×(−5)×(−2)=−120(-12) \times (-5) \times (-2) = -120

Explanation:

First, multiply the absolute values: 12×5×2=12012 \times 5 \times 2 = 120. Since there are three negative signs (which is an odd number), the final product is negative: −120-120.

Problem 2:

Evaluate using the distributive property: 26×(−48)+(−48)×(−36)26 \times (-48) + (-48) \times (-36).

Solution:

(−48)×[26+(−36)]=(−48)×(−10)=480(-48) \times [26 + (-36)] = (-48) \times (-10) = 480

Explanation:

Using the formula a×b+a×c=a×(b+c)a \times b + a \times c = a \times (b + c), we take a=−48a = -48, b=26b = 26, and c=−36c = -36. This simplifies the calculation to (−48)×(−10)(-48) \times (-10), resulting in a positive 480480 because the product of two negatives is positive.

Problem 3:

Determine the product of 1515 and −8-8.

Solution:

$$\begin{array}{r} 15 \\ \times (-8) \\ \hline -120 \end{array}$$

Explanation:

Multiply the positive integer 1515 by the negative integer −8-8. Since the signs are different, the product is negative: 15×8=12015 \times 8 = 120, so the result is −120-120.

Problem 4:

Find the value of (−1)×(−2)×(−3)×(−4)(-1) \times (-2) \times (-3) \times (-4).

Solution:

(−1)×(−2)×(−3)×(−4)=24(-1) \times (-2) \times (-3) \times (-4) = 24

Explanation:

There are four negative integers. Since 44 is an even number, the product will be positive. Calculating the absolute product: 1×2×3×4=241 \times 2 \times 3 \times 4 = 24.

Multiplication of Integers Class 7 Notes & Examples