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Verify whether the indicated numbers are zeros of the polynomials corresponding to them in the following cases: (i) f(x) = 3x + 1, x = \(\frac{-1}{3}\) (ii) f(x) = x2 – 1, x = 1,−1 (iii) g(x) = 3x2 – 2 , x = \(\frac{2}{\sqrt3}\) , \(\frac{-2}{\sqrt3}\) (iv) p(x) = x3 – 6x2 + 11x – 6 , x = 1, 2, 3 (v) f(x) = 5x – π, x = \(\frac{4}{5}\) (vi) f(x) = x2 , x = 0 (vii) f(x) = lx + m, x = \(\frac{-m}{l}\)(viii) f(x) = 2x + 1, x = \(\frac{1}{2}\) |
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Answer» (i) f(x) = 3x + 1, x = \(\frac{-1}{3}\) f(x) = 3x + 1 Substitute x = \(\frac{-1}{3}\) in f(x) \(f (\frac{-1}{3})\)= \(3(\frac{-1}{3}) + 1\) = -1 + 1 = 0 Since, the result is 0, so x = \(\frac{-1}{3}\) is the root of 3x + 1 (ii) f(x) = x2 – 1, x = 1,−1 f(x) = x2 – 1 Given that x = (1 , -1) Substitute x = 1 in f(x) f(1) = 12 – 1 = 1 – 1 = 0 Now, substitute x = (-1) in f(x) f(-1) = (−1)2 – 1 = 1 – 1 = 0 Since , the results when x = 1 and x = -1 are 0, so (1 , -1) are the roots of the polynomial f(x) = x2 – 1 (iii) g(x) = 3x2 – 2 , \(x = \frac{2}{\sqrt3}\) ,\(\frac{-2}{\sqrt3}\) g(x) = 3x2 – 2 Substitute \(x = \frac{2}{\sqrt3}\) in g(x) g\((\frac{2}{\sqrt3})\) = \(3(\frac{2}{\sqrt3})^2 - 2\) = \(3 (\frac{4}{3}) - 2\) = 4 – 2 = 2 ≠ 0 Now, Substitute x = \(\frac{-2}{\sqrt3}\) in g(x) \(g(\frac{2}{\sqrt3}) = 3 (\frac{-2}{\sqrt3})^2 - 2\) = \(3 (\frac{4}{3}) - 2\) = 4 – 2 = 2 ≠ 0 Since, the results when x = \(\frac{2}{\sqrt3}\) and x = \(\frac{-2}{\sqrt3}\) are not 0. Therefore (\(\frac{2}{\sqrt3}\) ,\(\frac{-2}{\sqrt3}\) ) are not zeros of 3x2 – 2. (iv) p(x) = x3 – 6x2 + 11x – 6 , x = 1, 2, 3 p(1) = 13 – 6(1)2 + 11 x 1 – 6 = 1 – 6 + 11 – 6 = 0 p(2) = 23 – 6(2)2 + 11 x 2 – 6 = 8 – 24 – 22 – 6 = 0 p(3) = 33 – 6(3)2 + 11 x 3 – 6 = 27 – 54 + 33 – 6 = 0 Therefore, x = 1, 2, 3 are zeros of p(x). (v) f(x) = 5x – π, x = \(\frac{4}{5}\) f( \(\frac{4}{5}\) ) = 5 x \(\frac{4}{5}\) – π = 4 – π ≠ 0 Therefore, x = \(\frac{4}{5}\) is not a zeros of f(x). (vi) f(x) = x2 , x = 0 f(0) = 02 = 0 Therefore, x = 0 is a zero of f(x). (vii) f(x) = lx + m, x = \(\frac{-m}{l}\) f( \(\frac{-m}{l}\) ) = l x \(\frac{-m}{l}\) + m = -m + m = 0 Therefore, x = \(\frac{-m}{l}\) is a zero of f(x). (viii) f(x) = 2x + 1, x = \(\frac{1}{2}\) f(\(\frac{1}{2}\)) = 2 x \(\frac{1}{2}\) + 1 = 1 + 1 = 2 ≠ 0 Therefore, x = \(\frac{1}{2}\) is not a zero of f(x). |
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