is this done by expanding or just simply the algebraic rule?
1. algebraic rule
(a+b+a-b) ( a+b-a+b) check my working!! hahahahas
or is it
2.algebraic rule
(a+b+a+b) (a+b-a-b)
3.expanding with algebraic rule
(a^2+2ab+b^2)-(a^2-2ab+b^2)
(a+b)^2 - (a-b)^2?
2008-03-23 6:31 am
回答 (13)
2008-03-23 5:06 pm
✔ 最佳答案
Question 1[ (a + b) - (a - b) ] [ (a + b) + (a - b) ]
(2 b) (2 a)
4 a b
Question 2
(2a + 2b) ( 0 )
0
Question 3
4 a b
2008-03-23 5:15 pm
(a + b)^2 - (a - b)^2
= (a + b)(a + b) - (a - b)(a - b)
= (a^2 + ab + ab + b^2) - (a^2 - ab - ab + b^2)
= a^2 + 2ab + b^2 - a^2 + 2ab - b^2
= a^2 - a^2 + 2ab + 2ab + b^2 - b^2
= 4ab
(answer 3)
= (a + b)(a + b) - (a - b)(a - b)
= (a^2 + ab + ab + b^2) - (a^2 - ab - ab + b^2)
= a^2 + 2ab + b^2 - a^2 + 2ab - b^2
= a^2 - a^2 + 2ab + 2ab + b^2 - b^2
= 4ab
(answer 3)
2008-03-23 6:38 am
3.expanding with algebraic rule
(a+b)^2 - (a-b)^2 =
(a^2+2ab+b^2)-(a^2-2ab+b^2)=
a^2+2ab+b^2-a^2+2ab-b^2=
4ab
(a+b)^2 - (a-b)^2 =
(a^2+2ab+b^2)-(a^2-2ab+b^2)=
a^2+2ab+b^2-a^2+2ab-b^2=
4ab
2016-04-04 1:56 pm
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2015-07-12 2:54 pm
(a+b)^2 = a^2 +2ab+b^2 this equation 1
(a-b)^2 = a^2 -2ab+b^2 this equation 2
(a+b)^2 - (a-b)^2 = equation 1 + equation 2
= a^2 +2ab+b^2 - (a^2 -2ab+b^2)
= a^2 +2ab+b^2-a^2+2ab-b^2
= 4 ab
(a-b)^2 = a^2 -2ab+b^2 this equation 2
(a+b)^2 - (a-b)^2 = equation 1 + equation 2
= a^2 +2ab+b^2 - (a^2 -2ab+b^2)
= a^2 +2ab+b^2-a^2+2ab-b^2
= 4 ab
2008-03-23 6:48 am
1st approach is more easy
(a+b)^2 - (a-b)^2
= (a+b+a-b) (a+b-a+b)
= (2a) (2b)
= 4ab
(a+b)^2 - (a-b)^2
= (a+b+a-b) (a+b-a+b)
= (2a) (2b)
= 4ab
2008-03-23 6:44 am
3 is correct and that equals 4ab.
2008-03-23 6:36 am
(a+b)² - (a-b)² =
a² + 2ab² + b² - (a² - 2ab + b²) =
a² + 2ab + b² - a² + 2ab - b² =
4ab
a² + 2ab² + b² - (a² - 2ab + b²) =
a² + 2ab + b² - a² + 2ab - b² =
4ab
2008-03-23 6:36 am
(a^2+b^2+2ab) -(a^2+b^2-2ab)
=a^2+b^2+2ab -a^2 - b^2+2ab
=4ab
thus the right approach is the third one you wrote
=a^2+b^2+2ab -a^2 - b^2+2ab
=4ab
thus the right approach is the third one you wrote
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