Đáp án:
`(a+b)(c+d)-(a+d)(b+c)=(a-c)(d-b)`
Giải thích các bước giải:
`(a+b)(c+d)-(a+d)(b+c)=(a-c)(d-b)`
Ta có:
`(a+b)(c+d)-(a+d)(b+c)`
`=ac+ad+bc+bd-(ab+ac+db+dc)`
`=ac+ad+bc+bd-ab-ac-db-dc`
`=ac-ac+bd-db+ad+bc-ab+dc`
`=(ac-ac)+(db-db)+(ad+bc-ab-dc)`
`=0+0+(ad+bc-ab-dc)`
`=ad+bc-ab-dc`
`=ad-ab+bc-dc`
`=a(d-b)+c(b-d)`
`=(a-c)(d-b)`
Vì `(a-c)(d-b)=(a-c)(d-b)`
`=>(a+b)(c+d)-(a+d)(b+c)=(a-c)(d-b)(ĐPCM)`
Vậy `(a+b)(c+d)-(a+d)(b+c)=(a-c)(d-b)`
