Answers

2014-02-18T18:57:08+01:00
Best way to solve this is to convert both roots to fractions:
1.2 equals  \frac{12}{10}
-0.4 equals  \frac{-4}{10}

Now, let's find the equation( in x) whose roots are  \frac{12}{10} and  \frac{-4}{10} !

It's either x equals  \frac{-4}{10} or x equals  \frac{12}{10}

Mathematically,
x= \frac{12}{10} or x= \frac{-4}{10}

x- \frac{12}{10} =0 or x+ \frac{4}{10} =0

(x- \frac{12}{10} )(x+ \frac{4}{10} )=0

Now clear brackets
x²+ \frac{4x}{10} - \frac{12x}{10} - \frac{48}{100} =0

Add like fractions
x²- \frac{8x}{10} - \frac{48}{100} =0

Then multiply through by 100 to clear fractions
100x²-80x-48=0

That is your equation! You can substitute either  \frac{12}{10} or  \frac{-4}{10} for x to check your answer.
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