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din culegerea mate 2000 consolidare de clasa a 8-a. am nevoie de niste ajutor:

d) 4(x + 5)²– (x - 1)²
e) (x² + 3x + 1)² – (x + 3)²
f) (x² + 2x – 3)² – (x - 1)²​


Răspuns :

d)  4(x + 5)²- (x - 1)² =

= [2(x + 5)]²- (x - 1)²

= [2(x + 5) - (x - 1)]·[2(x + 5) + (x - 1)]

= (2x+10-x+1)·(2x+10+x-1)

= (x+11)·(3x+9)

= 3·(x+11)·(x+3)

e)  (x² + 3x + 1)² - (x + 3)² =

= [(x² + 3x + 1) - (x + 3)]·[(x² + 3x + 1) + (x + 3)]

= (x²+3x+1-x-3)·(x²+3x+1+x+3)

= (x²+2x-2)·(x²+4x+4)

= (x²+2x-2)·(x+2)²

f)  (x² + 2x - 3)² - (x - 1)²​

= [(x² + 2x - 3) - (x - 1)]·[(x² + 2x - 3) + (x - 1)]

= (x²+2x-3-x+1)·(x²+2x-3+x-1)

= (x²+x-2)·(x²+3x-4)

= (x²+x-2)·(x-1)(x+4)

d) 4(x+5)^2 - (x-1)^2 = [(2(x+5) + (x-1)] [2(x+5) - (x-1)] = (2x+10+x-1)(2x+10-x+1) = (3x+9)(x+11) = 3(x+3)(x+11)

e) (x^2+3x+1)^2 - (x+3)^2 = (x^2+3x+1+x+3)(x^2+3x+1-x-3) = (x^2+4x+4)(x^2+2x-2) = (x+2)^2 × (x^2+2x-2)

f) (x^2+2x-3)^2 - (x-1)^2 = (x^2+2x-3+x-1)(x^2+2x-3-x+1) = (x^2+3x-4)(x^2+x-2) = (x-1)(x+4)(x^2+x-2)