Răspuns:
Explicație pas cu pas:
(fog)(x)=f(g(x))=f(x²+4x)=3·(x²+4x)+3=3x²+12x+3.
a) (fog)(4)=3·4²+12·4+3=3·16+48+3=48+51=99.
b) (fog)(x)=0, ⇒ 3x²+12x+3=0, |:3, ⇒ x²+4x+1=0, a=1, b=4, c=1
Δ=b²-4ac=4²-4·1·1=16-4=12=4·3, ⇒ √Δ=2√3.
x1=(-b-√Δ)/(2a)=(-4-2√3)/2=2·(-2-√3)/2=-2-√3.
x2=(-b+√Δ)/(2a)=(-4+2√3)/2=2·(-2+√3)/2=-2+√3.
S={-2-√3; -2+√3}
