2010 · Q16
If the equation (a2 +b2)x2 -2(ac+bd)x + (c2 +d2) = 0 has equal roots, then which one of the following is correct?
Elementary MathematicsAlgebra
- Aab = cd
- Bad = bc
- Ca2 + c2 =b2 +d2
- Dac = bd
Explanation
Zero discriminant gives (ac+bd)²=(a²+b²)(c²+d²), equality in Cauchy-Schwarz, so ad=bc.