Proof Without Words - Part 4

Algebra Level 1

The image above illustrates which identity?

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

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15 solutions

Trevor B.
Mar 6, 2014

The whole figure is a square with side length ( a + b ) . (a+b). The top left and bottom right rectangles both have length a a and height b , b, giving them an area of a b ab each and a total area of 2 a b . 2ab. The bottom left square has side length a , a, so its area is a 2 . a^2. The top right square has side length b , b, making its area b 2 . b^2.

The sum of all of these areas is equal to the area of the larger square with side length ( a + b ) , (a+b), which is ( a + b ) 2 . (a+b)^2. Therefore, ( a + b ) 2 = a 2 + 2 a b + b 2 \boxed{(a+b)^2=a^2+2ab+b^2}

The whole figure is divided into 4 4 parts. ( 2 2 squares and 2 2 rectangles)

Area of square:

With side a a = a 2 a^{2}

With side b b = b 2 b^{2}

There are two rectangles of same measurements. L e n g t h = a Length = a , B r e a d t h = b Breadth = b

Thus, area of 2 2 rectangles = 2 × ( l × b ) 2 \times (l \times b) = 2 a b 2ab

So, total area = a 2 + b 2 + 2 a b a^{2}+b^{2}+2ab

Thus, the answer to this question is the identity:

( a + b ) 2 = a 2 + 2 a b + b 2 \boxed{(a + b)^{2} = a^{2}+2ab+b^{2}}

Or else we can directly put the identity:

Side of square = a + b a + b

Area of square = ( a + b ) 2 = a 2 + 2 a b + b 2 \boxed{(a + b)^{2} = a^{2}+2ab+b^{2}}

Saurabh Mallik - 7 years, 1 month ago

Good pictorial depiction of a very basic formula. Great!!! The only regret is that had i got such things in my school days, I would have loved mathematics much more ! ;-)

Tanmay Meher - 7 years, 2 months ago

very well explained~ thanks :D

Heng Joe Kit - 7 years, 3 months ago

Yeah, that's the same idea I used... But did anyone use some other way to figure this out? Just curious... Really nice problem and solution, by the way. Thumbs up!

Kevin Mano - 7 years, 3 months ago

yep the same thing i got it !

vanshika shrisrimal - 7 years ago

excellent !!!

Thiên Trang - 7 years ago

False + Mean less problime.

محمد فكرى - 5 years, 5 months ago

The trick is just analyze that the image involves a quadratic sum: a^2 + ab + ab + b^2 = a^2 + 2ab + b^2 = (a+b)^2

whole figure is about area of square which have its side as (a+b)= area of square having side "a" + area of square having side "b" + area of two rectangles having respective area as "ab"...so the equation as follows

area of square (a+b)= (a+b)^2

area of square(a)= a^2

area of square (b)= b^2

area of two same rectangles = 2x(ab)

as per quatation

(a+b)^2= a^2 +b^2 +2ab

Ashish Chaurasiya - 7 years, 1 month ago

Excellent

parth limbachiya - 7 years, 1 month ago

The area of the small red square is b^2; the area of the rectangles is ‘ab’ and we have two of them hence total area is ‘2ab’; the area of big blue square is a^2. The sum of all this represent the area of the big square formed by these small shapes. The area of the big square is (a+b)^2.. so equate the sum of small parts to the whole

Sourav Hi
Mar 7, 2014

The whole figure is a square with side length (a+b). The top left and bottom right rectangles both have length a and height b giving them an area of ab each and a total area of 2ab The bottom left square has side length a so its area is a a The top right square has side length b making its area b b

The sum of all of these areas is equal to the area of the larger square with side length (a+b) which is (a+b)(a+b). Therefore, the answer is (a+b)(a+b)=a a+2ab+b b

Mostafa Algammal
Mar 31, 2014

Area sq = L^2 & L=a+b
so A=L^2=(a+b)^2 (a+b)^2= a^2 +b^2+2ab :)

Angelena Coralie
Mar 22, 2014

the surface of square is a^2....since a=a+b then the surface is (a+b)^2

Swagata Paul
Mar 11, 2014

The figure is a square of length a+b. Then total area=(a+b)^2=area of square of side a+2(area of rectangles of sides a and b)+ area of square of side b.

Como na imagem está expicitado que cada lado tem sua medida, fica fácil saber que o quadrado de maior lado é a² e o de menor lado é b², resta os retangulos que são iguais somando juntos 2ab, o que nos dá: a²+b²+2ab=(a+b)²

Sunny Patel
Mar 8, 2014

there are four areas are in figure = a^2 , b^2 , ab , ab

                 so total = (a+b)^ 2
Vaishnavi Gupta
Mar 8, 2014

Sum of: areas of 2 pink rectangles (ab +ab) + Area of red square (b^2) + Area of grey sq. (a^2) =Area of the biggest sq. (a+b)^2 Thus we get the required relation.

Ahsan Iqbal
Mar 11, 2014

Its a square one part is a another is b, So none hand is a+b and a+b, So area is (a+b)(a+b)= (a+b)2 = a2 +2ab+b2

Area of Square= s i d e 2 side^{2} ; Here we have four sides(one side = a+b) which are equal hence reprsents square as ( a + b ) 2 = a 2 + 2 a b + b 2 (a+b)^{2} = a^{2} +2ab + b^{2}

Aydan Chatman
Apr 6, 2020

the pink is b and a is blue so it is clearly divided wich is a2+2ab=b

Betty BellaItalia
Apr 21, 2017

Pratik Ingale
Jan 25, 2016

A and b together makes a side of square so we get l.h.s (a+b)^2 then area of 2nd large square whose side is a is a^2, add of area of rectangle having sides a and b is 2ab and smallest square having side b is b^2 so this makes whole eq

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