Sagot :

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C=4xau carre - 25+(2x+5)(4x-5)

C=(2x-5)(2x+5)+(2x+5)(4x-5)

facto :

(2x+5)(2x-5+4x-5)=

(2x+5)(6x-10)=

2(2x+5)(3x-5)

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