# function of x

• Jan 8th 2009, 09:17 AM
RubbishAtMaths
function of x
you are given that \$\displaystyle f(x)=x^3+kx+c\$ the value of f(0) is 6, and \$\displaystyle x - 2 \$ is a factor of f(x)

Find the values of k and c

ok i dont understand these at all, probably the last thing i have to revise and its my worst enemy. can someone explain??? thank yoouu (Wink)
• Jan 8th 2009, 09:32 AM
masters
Quote:

Originally Posted by RubbishAtMaths
you are given that \$\displaystyle f(x)=x^3+kx+c\$ the value of f(0) is 6, and \$\displaystyle x - 2 \$ is a factor of f(x)

Find the values of k and c

ok i dont understand these at all, probably the last thing i have to revise and its my worst enemy. can someone explain??? thank yoouu (Wink)

Hello Rubbish,

\$\displaystyle f(x)=x^3+kx+c\$

\$\displaystyle f(0)=6 \Longrightarrow 0^3+k(0)+c=6 \Longrightarrow \boxed{c=6}\$

If \$\displaystyle x-2\$ is a factor of \$\displaystyle f(x)=x^3+kx+c\$, then \$\displaystyle f(2)=0\$

\$\displaystyle f(2)=0 \Longrightarrow 2^3+2k+6=0 \Longrightarrow \boxed{k=-7}\$
• Jan 8th 2009, 09:36 AM
RubbishAtMaths
muchly obliged govener, think i get em now (Happy)