One of the roots of the equation 2 x 3 − 5 x 2 + 3 is 1 . The other 2 roots can be expressed as c a ± b . Find a + b + c .
(Please add a elegant and thorough solution)
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Given that we know that a root is 1, wouldn't it be easier to just find x − 1 2 x 3 − 5 x 2 + 3 = 2 x 2 − 3 x − 3 ?
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I did that actually. Then I noticed the question name is about Vieta
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It is given that 1 is one of the roots of 2 x 3 − 5 x 2 + 3 . Let the other two roots be α and β . Using Vieta's Formulas, we have:
( 1 ) ( α ) ( β ) = 2 − 3 ⇒ β = 2 α − 3
We also know that:
1 + α + β = 2 5 ⇒ α + β = 2 5 − 1 = 2 3 ⇒ α − 2 α 3 = 2 3
2 α 2 − 3 = 3 α ⇒ 2 α 2 − 3 α − 3 = 0
⇒ α = 2 ( 2 ) − ( − 3 ) ± ( − 3 ) 2 − 4 ( 2 ) ( − 3 ) = 4 3 ± 3 3 = c a ± b
⇒ a + b + c = 3 + 3 3 + 4 = 4 0