How do you find all the zeros of f(x) = 3x^2 − 4x − 15f(x)=3x2−4x−15?

2 Answers
Binayaka C.
Apr 7, 2018

Zeros of f(x)f(x) are x=3 and x= -5/3x=3andx=−53

Explanation:

f(x)=3x^2-4x-15 =3x^2-9x+5x-15f(x)=3x2−4x−15=3x2−9x+5x−15

=3x(x-3)+5(x-3)= (x-3)(3x+5)=3x(x−3)+5(x−3)=(x−3)(3x+5)

Zeros of f(x)f(x) are x=3 and x= -5/3x=3andx=−53 [Ans]

Bounce light knowledge
Apr 7, 2018

x=3,(-5)/3x=3,−53

Explanation:

Using trial and error method (x-3)(x−3) is a factor of f(x)f(x)
I.e(x-3), x=3(x−3),x=3
f(3)=3(3^2)-4(3)-15f(3)=3(32)−4(3)−15
=3(9)-12-15=3(9)−12−15
=27-12-15=27−12−15
=0=0
Using long division of polynomial's
(+)3x+5(+)3x+5
root(x-3)(3x^2-4x-15)x−3√3x2−4x−15
((-)3x^2-9x)/(5x-15)(−)3x2−9x5x−15
((-)5x-15)/(……)(−)5x−15……
Since xx is in the 2nd degree, the 2 factors of f(x)f(x)are (x-3)(x−3) and 3x+53x+5
Equating factor to zero.
x-3=0,3x+5=0x−3=0,3x+5=0
x=3,3x=-5x=3,3x=−5
x=3,x=(-5)/3x=3,x=−53(color (blue) (zero's. Of.f(x)))

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