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### Grade 7 - Mathematics4.11 Finding the value of (a+b) (a-b) (Geometrical Proof)

#### Find the vlaue of (a+b)(a-b)

Area of rectangle ACDH = AC * AH = (a+b) (a-b)Sq. Units   ..........I
But area of rectangle ACDH = Area of rectangle ACEG - Area of rectangle HDEG

= AC * AG - HD * HG
= (a+b)a - (a+b)b
= a2 + ab - ab -b2
= a2 - b2    ..........II
From I and II
(a+b) (a-b) = a2 - b2
Directions: Solve the following problems. Also write at least ten examples of your own.
 Q 1: (4x-4y) (4x+4y) = _____?16x2-16y216x2+16y2 Q 2: (17x-15y) (17x+15y) = _____?289x2+225y2289x2-225y2 Q 3: (6x-7y) (6x+7y) = _____?36x2+49y236x2-49y2 Q 4: (9x-7y) (9x+7y) = _____?81x2+49y281x2-49y2 Question 5: This question is available to subscribers only! Question 6: This question is available to subscribers only!

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