Question

F ( x ) = x ( x + 5 ) f ( x ) = 84

Answer 1

f(x)=x.(x+5)

f(x)=84

84=x.(x+5)

84=x²+5x

x²+5x-84=0

a=1, b=5, c=-84

Δ=b²-4ac
Δ=(5)²-4.1.(-84)
Δ=25+336
Δ=361

x'=(-b+√Δ)/2a
x'=(-5+√361)/2.1
x'=(-5+19)/2
x'=14/2
x'=7

x''=(-b-√Δ)/2a
x''=(-5-√361)/2.1
x''=(-5-19)/2
x''=-24/2
x''=-12

x=7 ou x=-12