Question

Rezolvati :(x+1)(x+2)=56

Answer 1

(x+1)(x+2)=56

7×8 = 56  => x = 6 

(-8)×(-7) = 56 => x = -9

Answer 2

(x+1)(x+2)=56
x²+2x+x+2=56
x²+3x-54=0
Δ=b²-4ac⇒Δ=225
x1 si x2=-b+ si - √delta/2a=-3 = sau - √225/2⇒
⇒x1=-3+15-2/2=6
deci x1=6
⇒x2=-3-15-18/2=-9
deci x2=-9
de unde S-(x1, x2)={6, -9}

sau mai usor
x+1 si x+2 sunt numere consecutive si x+1 mai mic decat x+2
de unde (x+1)(x+2)=56 adica 7*8
⇒ daca x+1=7 
x=6
⇒x+2=8
x=6 s.m.d