P(x)= (x-a)(x-10)(x-20)+15. Given that p(7)=15.... what is the value of a?
(Seems like no one want to answer the question after half a day then)
Your entry:P(x)=(x-a)(x-10)(x-20). Given that P(7)=15, what is the value of a?
Lets expand the polynomial P(x) first:
\(P(x)=\left(x-a\right)\left(x-10\right)\left(x-20\right)+15\)
\(=\left(x-a\right)\left(x^2-30x+200\right)\)
\(P(7)=15\)
Plug x=7 into P(x)
\(P(7)=(7-a)(7^2-30\cdot 7+200)=15\)
\(=(7-a)(49-210+200)\)
\(=39(7-a)\)
\(=273-39a\)
We know that \(273-39a=15\)
\(a=-(15-273)/39\)
\(a=-288/39=-96/13\)
P(x)= (x-a)(x-10)(x-20)+15. Given that p(7)=15....
what is the value of a?
\(\begin{array}{|rcll|} \hline P(x) &=& (x-a)(x-10)(x-20)+15 \quad & | \quad x = 7 \\\\ P(7) &=& (7-a)(7-10)(7-20)+15 \quad & | \quad P(7) = 15 \\ 15 &=& (7-a)(7-10)(7-20)+15 \quad & | \quad -15 \\ 0 &=& (7-a)(7-10)(7-20) \\\\ 0 &=& (7-a)(-3)(-13) \\ 0 &=& (7-a)\cdot 3\cdot 13 \\ 0 &=& (7-a)\cdot 39 \quad & | \quad :39 \\ 0 &=& (7-a)\cdot 1 \\ 0 &=& 7-a \\ a &=& 7 \\ \hline \end{array}\)