Trik Jitu #9 - Persamaan Kuadrat

$latex Jumlah\ dari\ kebalikan\ akar-akar\ persamaan\ kuadrat\ ax^2+bx+c=0\\ditentukan\ oleh\ {\color{red}\frac{1}{x_{1}}+\frac{1}{x_{2}}=-\frac{b}{c}}.$

Contoh:

$latex Jumlah\ kebalikant\ akar-akar\ persamaan\ 3x^2-9x+4=0\ adalah\ ....\\\\A.\ \ -\frac{4}{9}\\\\B.\ \ -\frac{3}{4}\\\\C.\ \ -\frac{9}{4}\\\\D.\ \ \frac{9}{4}\\\\E.\ \ \frac{3}{4}$

Jawaban: D
$latex \Large \begin{array}{rcl}\frac{1}{x_{1}}+\frac{1}{x_{2}}&=&-\frac{b}{c}\\\\&=&-\frac{-9}{4}\\\\&=&\frac{9}{4}\end{array}$

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