Algebra Questions

Multiple choice
  1. $\cfrac {\sqrt {61}}{9}$
  2. $\cfrac {2\sqrt 17}{9}$
  3. $\cfrac {\sqrt {34}}{9}$
  4. $\cfrac {2\sqrt 13}{9}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

p, q, r in AP implies 2q = p + r. Roots alpha, beta satisfy alpha+beta = -q/p and alpha*beta = r/p. 1/alpha + 1/beta = (alpha+beta)/(alpha*beta) = (-q/p) / (r/p) = -q/r = 4. So q = -4r. Since 2q = p + r, -8r = p + r, so p = -9r. Roots are alpha, beta of px^2 + qx + r = 0, which is -9rx^2 - 4rx + r = 0. Divide by -r: 9x^2 + 4x - 1 = 0. Roots = (-4 +/- sqrt(16 - 4*9*(-1))) / 18 = (-4 +/- sqrt(52)) / 18 = (-4 +/- 2*sqrt(13)) / 18 = (-2 +/- sqrt(13)) / 9. Difference = |alpha - beta| = (2*sqrt(13)) / 9.

Multiple choice
  1. $\displaystyle \left ( \frac{b_{1}}{b_{2}} \right )^{2} = \frac{a_{2} c_{2}}{a_{1} c_{1}}$
  2. $\displaystyle \left ( \frac{c_{1}}{c_{2}} \right )^{2} = \frac{b_{1} c_{2}}{c_{1} b_{2}}$
  3. $\displaystyle \left ( \frac{a_{1}}{a_{2}} \right )^{2} = \left ( \frac{c_{1}}{c_{2}} \right )^{2}$
  4. $\displaystyle \left ( \frac{b_{1}}{b_{2}} \right )^{2} = \frac{a_{1} c_{1}}{a_{2} c_{2}}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For a quadratic equation ax^2 + bx + c = 0, if the ratio of roots is k, then (r1/r2) = k. The condition for equal ratios of roots for two equations is (b1/b2)^2 = (a1*c1)/(a2*c2).