Question

Calcule (r+5)(r-3)=

Answer 1

r²-3r+5r-15=0
r²+2r-15=0
∆= (2)²-4(1)(-15)
∆= 4+60
∆=64

X= -2±√64/2.1
X= -2±8/2

X1= -2+8/2
X1= 3

X2= -2-8/2
X2= -5