The formula for the difference of squares

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Difference of Squares Formula

The difference of squares formula is another key algebraic shortcut that simplifies expressions involving two squared terms subtracted from each other. It is written as:

(XY)2=X22XY+Y2(X - Y)^2=X^2 - 2XY + Y^2
This formula skips the need for full expansion and directly factors the expression. It works for both numerical and algebraic expressions, making it versatile in solving equations and simplifying terms. That is, when we encounter two numbers with a minus sign between them, that is, the difference and they will be in parentheses and raised as a squared expression, we can use this formula.

For (xy)2(x - y)^2 the full expansion would be:
(xy)2=(xy)(xy)=xx+x(y)yxy(y)=x22xy+y2(x - y)^2=(x-y)(x−y)=x⋅x+x⋅(-y)-y⋅x−y⋅(-y)=x^2-2xy+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

Example:

(a4)2=(a - 4)^2=
a×a+a×(4)+(4)×a+(4)×(4)=a\times a+a\times (-4)+ (-4)\times a + (-4) \times (-4) =
a2+2(4a)+(4)2=a^2+2(-4a)+ (-4)^2 =
a28a+16a^2-8a+16

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Test yourself on square of difference!

einstein

\( (4b-3)(4b-3) \)

Rewrite the above expression as an exponential summation expression:

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Pay attention - The formula also works in non-algebraic expressions or combinations with numbers and unknowns.

Let's look at an example

(X7)2=(X-7)^2=
Here we identify two elements between which there is a minus sign and they are enclosed in parentheses and raised to the square as a single expression.
Therefore, we can use the formula for the difference of squares.
We will work according to the formula and pay attention to the minus and plus signs.
We will obtain: 
(X7)2=x214x+49(X-7)^2=x^2-14x+49
Indeed, we pronounce the same expression differently using the formula.


If you are interested in this article, you might also be interested in the following articles:

Square

The area of a square

Multiplication of the sum of two elements by the difference between them

The formula for the sum of squares

The formulas that refer to two expressions to the power of 3

In the blog of Tutorela you will find a variety of articles about mathematics.


Examples and exercises with solutions of the difference of squares formula

Exercise #1

(4b3)(4b3) (4b-3)(4b-3)

Rewrite the above expression as an exponential summation expression:

Video Solution

Step-by-Step Solution

To solve this problem, we will apply the square of a binomial formula.

The given expression is (4b3)(4b3)(4b-3)(4b-3). We recognize this as the square of a binomial, which can be rewritten as (4b3)2(4b-3)^2. To expand this expression, we use the formula:

(ab)2=a22ab+b2(a-b)^2 = a^2 - 2ab + b^2

In our expression, a=4ba = 4b and b=3b = 3. Let's apply the formula:

  • Calculate a2a^2:
    a2=(4b)2=16b2a^2 = (4b)^2 = 16b^2
  • Calculate 2ab-2ab:
    2ab=2(4b)(3)=24b-2ab = -2(4b)(3) = -24b
  • Calculate b2b^2:
    b2=(3)2=9b^2 = (3)^2 = 9

Putting it all together, we have:

(4b3)2=16b224b+9(4b-3)^2 = 16b^2 - 24b + 9

Therefore, the exponential summation expression is (4b3)2(4b-3)^2, with the expanded form:

16b224b+916b^2 - 24b + 9

This matches choice 3, confirming our solution.

Answer

(4b3)2 (4b-3)^2

16b224b+9 16b^2-24b+9

Exercise #2

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

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

Video Solution

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)

Exercise #3

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

Video Solution

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

Exercise #4

Declares the given expression as a sum

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

Video Solution

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

Exercise #5

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

(xy)2 (x-y)^2

Video Solution

Step-by-Step Solution

We use the abbreviated multiplication formula:

(xy)(xy)= (x-y)(x-y)=

x2xyyx+y2= x^2-xy-yx+y^2=

x22xy+y2 x^2-2xy+y^2

Answer

x22xy+y2 x^2-2xy+y^2

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