Trik Jitu #18 - Fungsi Kuadrat

$latex Nilai\ minimum\ (atau\ maksimum)\ fungsi\ {\color{red}y=f(x)=ax^2+bx+c}\\terjadi\ pada\ {\color{red}x=-\frac{b}{2a}}.$

Contoh:
$latex Nilai\ minimum\ fungsi\ yang\ ditentukan\ oleh\ rumus\\f(x)=2x^2-8x+p\ adalah\ 20.\ Nilai\ f(2)\ adalah\ ....\\A.\ \ -28\\B.\ \ -20\\C.\ \ 12\\D.\ \ 20\\E.\ \ 28$

Jawaban: C
$latex \begin{array}{rcl}x&=&-\frac{b}{2a}\\\\&=&-\frac{-8}{2(2)}\\\\&=&\frac{8}{4}\\\\&=&2\end{array}$

$latex Nilai\ minimum\ fungsi\ itu\ terjadi\ pada\ x=2.\ Jadi\ f(2)=20.$

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