Question

Aflati nr.nat n,stiind ca n×(n+1)=72.
dau 20 puncte ajutati va rogg mult​

Answer 1

n(n+1)=72

n²+n=72

n²+n-72=0

a=1, b=1, c=-72

∆=√b²-4ac = √1-4×1×(-72) = √1+288 = √289 = 17

∆>0 =>

x₁=(-b+√∆)/2 <=> n₁ = (-1+17)/2 = 16/2=8

x₂=(-b-√∆)/2 <=> n₂ = (-1-17)/2 = -18/2=-9

Proba:

8(8+1)=8×9=72

-9(-9+1)=-9×(-8)=72