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Roots and Coefficients - Practice Questions
Question 1 of 19The cubic polynomial \(P(x) = {x^3} + a{x^2} + bx + c\), where \(a\), \(b\) and \(c\) are real numbers has three real zeros, \(1\), \(\alpha \) and \(\dfrac{1}{\alpha }\). The value of \(a + b\) is?
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Roots and Coefficients - Practice Questions
Question 2 of 19It is known that two of the roots of the equation: \(2{x^3} - 2{x^2} - kx + 6 = 0\) are equal in value but opposite in sign. Find the value of \(k\).
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Roots and Coefficients - Practice Questions
Question 3 of 19\(P(x) = {x^3} - 6{x^2} + 11x - 6\) has one of the roots equal to the sum of the other two roots. The values of the three roots are?
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Roots and Coefficients - Practice Questions
Question 4 of 19If \(\alpha \) and \(\beta \) are the roots of the equation \({x^2} + 4x - 2 = 0\), then the quadratic equation whose roots are \(\dfrac{\alpha }{\beta }\) and \(\dfrac{\beta }{\alpha }\) is?
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Roots and Coefficients - Practice Questions
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Roots and Coefficients - Practice Questions
Question 6 of 19If \(\alpha \) and \(\beta \) are the roots of the \({x^2} + 8x - 5 = 0\),find the quadratic equation whose roots are \(\dfrac{\alpha }{\beta }\) and \(\dfrac{\beta }{a}\).
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Roots and Coefficients - Practice Questions
Question 7 of 19One of the roots of \(P(x) = {x^3} + p{x^2} + 1\) is equal to the sum of the other two roots of \(P(x)\).Find the value of \(p\).
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Roots and Coefficients - Practice Questions
Question 8 of 19The polynomial \(P(x) = {x^3} - {x^2} + 4x - 6\) has roots \(\alpha \),\(\beta \) and \(\gamma \).
Evaluate:
\(i)\,\alpha + \beta + \gamma \)
\(ii)\,\alpha \beta \gamma \)
\(iii)\,\dfrac{1}{{\alpha \beta }} + \dfrac{1}{{\beta \gamma }} + \dfrac{1}{{\alpha \gamma }}\)
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Roots and Coefficients - Practice Questions
Question 9 of 19The polynomial \(P(x)\) is given by \(P(x) = p{x^3} - 8{x^2} + qx - 32\), where \(p\) and \(q\) are constants. The three zeros of \(P(x)\) are \(-2,4\) and \(\alpha\). Find the value of \(\alpha\).
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Roots and Coefficients - Practice Questions
Question 10 of 19The polynomial \(P(x) = 10x^3 - 39x^2 + ax+b = 0\) has a zero at \(x = 1\) and the remaining zeros are reciprocals of each other.
i) Find the values of \(a\) and \(b\).
ii) Find all the zeros of the polynomial.
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Roots and Coefficients - Practice Questions
Question 11 of 19The polynomial \(P(x) = 9x^4 + 9x^3 - 25x^2 - 27x -6\) has the roots \(\alpha,\, \beta,\,\gamma,\, \delta\). Given the condition that \(\alpha + \beta = 0\),
i) Show that \(\gamma + \delta = -1\)
ii) By considering the sum of the roots three at a time show that \(-\beta^2(\gamma + \delta) = 3\)
iii) By considering the sum of the roots two at a time show that \(-\beta^2 + \gamma\delta = \dfrac{-25}{9}\)
iv) Hence or otherwise determine the roots of \(P(x)\)AnswerYou must be logged in to see the answer.You must be logged in to see the worked solutions.You must have an active subscription to access course content
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Roots and Coefficients - Practice Questions
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Roots and Coefficients - Practice Questions
Question 13 of 19The polynomial \(P(x) = x^4 + 4x^3 + x^2 -6x + 2\) has roots; \(\alpha,\, \beta,\, \gamma,\, \delta\). Given the condition that \(\alpha\beta = -1\):
i) Show that \(\gamma\delta = -2\).
ii) By considering the sum of the roots show that \(\gamma + \delta = -4-(\alpha+\beta)\).
iii) By considering the sum of the roots three at a time show that \(\gamma + \delta = -6-2(\alpha+\beta)\).
iv) Hence or otherwise determine the roots of \(P(x)\)
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Roots and Coefficients - Practice Questions
Question 14 of 19The \(\alpha, \beta, \delta\) are the roots of \(x^3 -x+1 = 0\) find the value of \[\left(\alpha + \frac{1}{\beta} \right)\left(\beta + \frac{1}{\delta} \right)\left(\delta + \frac{1}{\alpha} \right)\]
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Roots and Coefficients - Practice Questions
Question 15 of 19The polynomial \(P(x) = 8x^3 - 12x^2 -2x+3\) has roots forming consecutive terms of an arithmetic sequence. Find these roots.
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Roots and Coefficients - Practice Questions
Question 16 of 19The polynomial \(P(x) = 24x^3 - 38x^2 + 19x - 3\) has roots forming consecutive terms of a geometric sequence. Find these roots.
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Roots and Coefficients - Practice Questions
Question 17 of 19If \(\alpha\) and \(\beta\) are the roots of the equation \(x^2 + mx+n = 0\), find the roots of \(nx^2-mx+1 = 0\) in terms of \(\alpha\) and \(\beta\).
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Roots and Coefficients - Practice Questions
Question 18 of 19Express \(\cos 3\theta = -\frac{1}{2}\) in terms of \(\cos \theta\) and by letting \(x = \cos\theta\) show that \(\cos 3\theta = -\frac{1}{2}\) can be expressed as
\[8x^3-6x+1=0\]
Hence deduce that:
i) \(\displaystyle \cos \frac{\pi}{9} = \cos \frac{2\pi}{9} + \cos\frac{4\pi}{9}\)
ii) \(\displaystyle \sec\frac{\pi}{9}\sec\frac{2\pi}{9}\sec\frac{4\pi}{9} = 8\)
iii) \(\displaystyle \tan^2\frac{\pi}{9}+\tan^2\frac{2\pi}{9}+\tan^2\frac{4\pi}{9} = 33\)
NOTE: This is a very challenging and hard question
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Roots and Coefficients - Practice Questions
Question 19 of 19i) Prove that \( \displaystyle \tan 3\theta = \frac{3\tan\theta - \tan^3\theta}{1-3\tan^2\theta}\)
ii) Let \(x =\tan\theta\), hence find the three roots of \( \displaystyle x^3-3x^2-3x+1=0\)
iii) Find the value of
\((\alpha)\quad\displaystyle \tan \frac{\pi}{12}+\tan\frac{5\pi}{12}\)
\((\beta)\quad\displaystyle \tan\frac{\pi}{12}\times\tan\frac{5\pi}{12}\)
Note: this is a very hard and challenging question
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