Short Multiplication Formulas - Examples, Exercises and Solutions

Understanding Short Multiplication Formulas

Complete explanation with examples

What are Abbreviated Multiplication Formulas?

Abbreviated multiplication formulas, also known as algebraic identities, are shortcuts that simplify the process of expanding and factoring expressions. These formulas save time and reduce the steps required for complex calculations. Abbreviated multiplication formulas will be used throughout our math studies, from elementary school to high school. In many cases, we will need to know how to expand or add these equations to arrive at the solution to various math exercises.

Abbreviated Multiplication Formulas for 2nd degree

Here are the basic formulas for abbreviated multiplication:

The square of the sum:
(X+Y)2=X2+2XY+Y2(X + Y)^2=X^2+ 2XY + Y^2

The squared difference:

(XY)2=X22XY+Y2(X - Y)^2=X^2 - 2XY + Y^2

The difference of squares:

(X+Y)×(XY)=X2Y2(X + Y)\times (X - Y) = X^2 - Y^2

Visual breakdown of abbreviated multiplication formulas: (a+b)² = a² + 2ab + b² and (a−b)² = a² − 2ab + b², with color-coded area models representing the expansion of binomials


Abbreviated Multiplication Formulas for 3rd degree

Abbreviated multiplication formulas for 3rd-degree expressions, also known as cubic identities, build upon the concepts of the 2nd-degree formulas we’ve already covered. The key difference is the adjustment for working with cubic (3rd-degree) terms instead of quadratic (2nd-degree) terms. These formulas simplify complex cubic expressions, breaking them into manageable parts to make calculations faster and more efficient. They are particularly useful in solving problems involving volumes of cubes and other 3D shapes or in advanced mathematics, such as polynomial factoring and equation solving.

Here are two of the most common abbreviated multiplication formulas for 3rd-degree expressions:

Cube of a Sum

(a+b)3=a3+3a2b+3ab2+b3(a+b)^3=a^3+3a^2 b+3ab^2+b^3

Cube of a Difference

​​​​​​​(ab)3=a33a2b+3ab2b3​​​​​​​(a-b)^3=a^3-3a^2 b+3ab^2-b^3


Abbreviated Multiplication Formulas Verification and Examples

We will test the shortcut multiplication formulas by expanding the parentheses.

Square of a Sum:

(X+Y)2=(X+Y)×(X+Y)=(X + Y)^2 = (X + Y)\times (X+Y) =

X2+XY+YX+Y2=X^2 + XY + YX + Y^2=

Since: XY=YXXY = YX

X2+2XY+Y2X^2 + 2XY + Y^2

Example:

(x+3)2 (x+3)^2

(x+3)2=x2+2(x)(3)+32=x2+6x+9 (x+3)^2=x^2+2(x)(3)+3^2=x^2+6x+9


Square of a Difference:

(XY)2=(XY)×(XY)=(X - Y)^2 = (X - Y)\times (X-Y) =

X2XYYX+Y2=X^2 - XY - YX + Y^2=

Since:XY=YX XY = YX

X22XY+Y2X^2 - 2XY + Y^2

Example:

(x4)2 (x−4)^2

(x4)2=x22(x)(4)+42=x28x+16 (x−4)^2=x^2−2(x)(4)+4^2=x^2−8x+16


Product of a Sum and a Difference:

(X+Y)×(XY)=(X + Y)\times (X-Y) =

X2XY+YXY2=X^2 - XY + YX - Y^2=

Since: XY=YX XY = YX

XY+YX=0 - XY + YX = 0

X2Y2X^2 - Y^2

Example:

(x+5)(x5) (x+5)(x−5)

(x+5)(x5)=x252=x225 (x+5)(x−5)=x^2−5^2=x^2−25


Using Abbreviated Multiplication Formulas to Shift the Expression Both Ways

It’s important to remember that these formulas are not one-sided; you can use them to switch between different forms of an expression as needed. For example, you can use the formula:

(X+Y)2=X2+2XY+Y2(X + Y)^2=X^2+ 2XY + Y^2

to expand an expression in parentheses into its expanded form. Conversely, if you encounter an expression like

X2+2XY+Y2X^2+ 2XY + Y^2

you can factor it back into

(X+Y)2(X + Y)^2

This flexibility allows you to work with the representation that is most useful for the problem at hand, whether it’s simplifying, solving, or analyzing the expression. Understanding this two-way functionality is essential for mastering algebraic manipulation.

Detailed explanation

Practice Short Multiplication Formulas

Test your knowledge with 48 quizzes

\( 4x^2+20x+25= \)

Examples with solutions for Short Multiplication Formulas

Step-by-step solutions included
Exercise #1

Declares the given expression as a sum

(7b3x)2 (7b-3x)^2

Step-by-Step Solution

To solve for (7b3x)2(7b - 3x)^2 as a sum, we'll follow these steps:

  • Step 1: Identify the given expression and apply the formula for the square of a difference:
    (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2 where a=7ba = 7b and b=3xb = 3x.
  • Step 2: Expand each term:
    • a2=(7b)2=49b2a^2 = (7b)^2 = 49b^2
    • 2ab=2×7b×3x=42bx-2ab = -2 \times 7b \times 3x = -42bx
    • b2=(3x)2=9x2b^2 = (3x)^2 = 9x^2
  • Step 3: Combine all terms to form the sum:
    (7b3x)2=49b242bx+9x2 (7b - 3x)^2 = 49b^2 - 42bx + 9x^2 .

Therefore, the solution to the problem is (7b3x)2=49b242bx+9x2(7b - 3x)^2 = 49b^2 - 42bx + 9x^2.

Hence, the correct answer choice is: 49b242bx+9x2 49b^2 - 42bx + 9x^2

Answer:

49b242bx+9x2 49b^2-42bx+9x^2

Video Solution
Exercise #2

(xx2)2= (x-x^2)^2=

Step-by-Step Solution

To solve the expression (xx2)2(x-x^2)^2, we will use the square of a binomial formula (ab)2=a22ab+b2(a-b)^2 = a^2 - 2ab + b^2.

Let's identify aa and bb in our expression:

  • Here, a=xa = x and b=x2b = x^2.

Applying the formula:

(xx2)2=(x)22(x)(x2)+(x2)2(x - x^2)^2 = (x)^2 - 2(x)(x^2) + (x^2)^2

Calculating each part, we get:

  • (x)2=x2(x)^2 = x^2
  • 2(x)(x2)=2x3-2(x)(x^2) = -2x^3
  • (x2)2=x4(x^2)^2 = x^4

Combining these results, the expression simplifies to:

x42x3+x2x^4 - 2x^3 + x^2

Therefore, the expanded form of (xx2)2(x-x^2)^2 is x42x3+x2\boxed{x^4 - 2x^3 + x^2}.

Answer:

x42x3+x2 x^4-2x^3+x^2

Video Solution
Exercise #3

Choose the expression that has the same value as the following:

(x7)2 (x-7)^2

Step-by-Step Solution

To solve the problem, we need to expand the expression (x7)2(x-7)^2 using the formula for the square of a difference.

The formula for the square of a difference is (ab)2=a22ab+b2(a-b)^2 = a^2 - 2ab + b^2.

Let's apply this formula to our expression (x7)2(x-7)^2:

  • Identify a=xa = x and b=7b = 7.
  • Substitute these values into the formula: (x7)2=x22(x)(7)+72(x-7)^2 = x^2 - 2(x)(7) + 7^2.
  • Calculate each term:
    • x2x^2 remains as x2x^2.
    • 2(x)(7)=14x-2(x)(7) = -14x.
    • 72=497^2 = 49.

So, expanding the expression, we get x214x+49x^2 - 14x + 49.

Thus, the expression that has the same value as (x7)2(x-7)^2 is x214x+49x^2 - 14x + 49.

Answer:

x214x+49 x^2-14x+49

Video Solution
Exercise #4

(a4)(a4)=? (a-4)(a-4)=\text{?}

Step-by-Step Solution

To solve the problem, we will expand the expression (a4)(a4)(a-4)(a-4) using the square of a difference formula.

This formula states: (xy)2=x22xy+y2(x-y)^2 = x^2 - 2xy + y^2.
In our case, x=ax = a and y=4y = 4, so we apply the formula:

  • First term: x2=a2x^2 = a^2
  • Second term: 2xy=2a4=8a-2xy = -2 \cdot a \cdot 4 = -8a
  • Third term: y2=42=16y^2 = 4^2 = 16

Putting it all together, the expression becomes:
a28a+16a^2 - 8a + 16.

After matching this result with the given choices, we find it corresponds to choice 4.

Therefore, the solution to the problem is a28a+16\mathbf{a^2 - 8a + 16}.

Answer:

a28a+16 a^2-8a+16

Video Solution
Exercise #5

Rewrite the following expression as an addition and as a multiplication:

(3xy)2 (3x-y)^2

Step-by-Step Solution

To solve this problem, let's start by identifying the parts of the binomial:

  • The expression (3xy)2(3x-y)^2 represents a binomial squared.
  • We recognize it has the form (ab)2(a-b)^2 where a=3xa = 3x and b=yb = y.
  • Using the formula for the square of a difference: (ab)2=a22ab+b2(a-b)^2 = a^2 - 2ab + b^2, we find the expanded form.

Let's apply the formula:

Step 1: Expand (3xy)2(3x-y)^2 using the formula:
(3xy)2=(3x)22(3x)(y)+y2(3x-y)^2 = (3x)^2 - 2(3x)(y) + y^2

Step 2: Calculate each part:
(3x)2=9x2(3x)^2 = 9x^2
2(3x)(y)=6xy-2(3x)(y) = -6xy
y2y^2 stays as y2y^2

Step 3: Combine these results to get the addition form:
9x26xy+y29x^2 - 6xy + y^2

The expression in multiplication form, as provided, is just repeating the factors:
(3xy)(3xy)(3x-y)(3x-y)

Therefore, the expression rewritten as addition is 9x26xy+y29x^2 - 6xy + y^2 and as multiplication (3xy)(3xy)(3x-y)(3x-y).

Answer:

9x26xy+y2 9x^2-6xy+y^2

(3xy)(3xy) (3x-y)(3x-y)

Video Solution

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