Examples with solutions for Difference of squares: Worded problems

Exercise #1

The length of the side of the square is x+1 x+1 cm

(x>3)

If we extend one side by 1 cm and shorten an adjacent side by 1 cm, we obtain a rectangle

Determine the area of the rectangle?

Video Solution

Step-by-Step Solution

First, recall the formula for calculating the area of a rectangle:

The area of a rectangle (which has two pairs of equal opposite sides and all angles are 90° 90\degree ) with sides of length a,b a,\hspace{4pt} b units, is given by the formula:

S=ab \boxed{ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=a\cdot b } (square units)

90°90°90°bbbaaabbbaaa

Proceed to solve the problem:

Calculate the area of the rectangle whose vertices we'll mark with letters EFGH EFGH (drawing)

It is given in the problem that one side of the rectangle is obtained by extending one side of the square with side length x+1 x +1 (cm) by 1 cm, and the second side of the rectangle is obtained by shortening the adjacent side of the given square by 1 cm:

(x+1)-1(x+1)-1(x+1)-1(x+1)+1(x+1)+1(x+1)+1(x+1)-1(x+1)-1(x+1)-1(x+1)+1(x+1)+1(x+1)+1x+1x+1x+1x+1x+1x+1x+1x+1x+1x+1x+1x+1HHHEEEFFFGGG

Therefore, the lengths of the rectangle's sides are:

EF=HG=(x+1)+1EF=HG=x+2EH=FG=(x+1)1EH=FG=x EF=HG=(x+1)+1\\ \downarrow\\ \boxed{ EF=HG=x+2}\\ \hspace{2pt}\\ \\ EH=FG=(x+1)-1\\ \downarrow\\ \boxed{ EH=FG=x } (cm)

Apply the above formula to calculate the area of the rectangle that was formed from the square in the way described in the problem:

S=EFEHS=(x+2)x S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=EF\cdot EH\\ \downarrow\\ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=(x+2)x (sq cm)

Continue to simplify the expression that we obtained for the rectangle's area, using the distributive property:

(m+n)d=md+nd (m+n)d=md+nd Therefore, applying the distributive property, we obtain the following area for the rectangle:

S=(x+2)xS=x2+2x S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=(x+2)x \\ \boxed{ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=x^2+2x} (sq cm)

The correct answer is answer B.

Answer

x2+2x x^2+2x

Exercise #2

If the length of the side of a square is X cm

(x>3)

Extend one side by 3 cm and shorten an adjacent side by 3 cm in order to obtain a rectangle.

Express the area of the rectangle using x.

Video Solution

Step-by-Step Solution

First, let's recall the formula for calculating the area of a rectangle:

The area of a rectangle (which has two pairs of equal opposite sides and all angles are 90° 90\degree ) with sides of length a,b a,\hspace{4pt} b units, is given by the formula:

S=ab \boxed{ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=a\cdot b } (square units)

90°90°90°bbbaaabbbaaa

With this is mind, let's proceed to solve the problem:

Calculate the area of the rectangle whose vertices we'll mark with letters EFGH EFGH

We are told that one side of the rectangle is obtained by extending one side of the square with side length x x (cm) by 3 cm, and the second side of the rectangle is obtained by shortening the adjacent side of the given square by 3 cm:

x-3x-3x-3x+3x+3x+3x-3x-3x-3x+3x+3x+3HHHEEEFFFGGG

Therefore, the lengths of the rectangle's sides are:

EF=HG=x+3EH=FG=x3 EF=HG=x+3\\ EH=FG=x-3 cm,

Apply the above formula in order to calculate the area of the rectangle that was formed from the square as described in the question:

S=EFEHS=(x+3)(x3) S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=EF\cdot EH\\ \downarrow\\ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=(x+3)(x-3) (sq cm)

Continue to simplify the expression that we obtained for the rectangle's area, using the difference of squares formula:

(c+d)(cd)=c2d2 (c+d)(c-d)=c^2-d^2 The area of the rectangle using the above formula is as follows:

S=(x+3)(x3)S=x232S=x29 S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=(x+3)(x-3) \\ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=x^2-3^2\\ \boxed{ S_{\textcolor{blue}{\boxed{\hspace{6pt}}}}=x^2-9} (sq cm)

Therefore, the correct answer is answer C.

Answer

x29(cm2) x^2-9\left(\operatorname{cm}²\right)

Exercise #3

The length of the square is equal to x x cm

(x>1) We extend one side by 3 cm and shorten an adjacent side by 1 cm and we obtain a rectangle,

What is the length of the side of the given square if it is known that the two areas are equal?

Video Solution

Answer

x=32cm x=\frac{3}{2}cm

Exercise #4

The side length of a square is X cm

(x>3)

We extend one side by 3 cm and shorten an adjacent side by 3 cm, and we get a rectangle.

Which shape has a larger area?

Video Solution

Answer

The square