Question

sendo a função f: IR → IR, definida por f(x) x² -x-20. calcule.

Answer 1

f(x)=x²-x-20

x²-x-20
-b ±√b²-4ac/2a
-(-1)±√(-1)²-4.1.(-20)/2.1
1±√1+80/2
1±√81/2
x'=1+9/2=10/2=5
x"=1-9/2=-8/2=-4
substituindo
f(5)=x²-x-20
f(5)=(5)²-(5)-20
f(5)=25-5-20
f(5)=0

f(-4)=x²-x-20
f(-4)=(-4)²-(-4)-20
f(-4)=16+4-20
f(-4)=0