Question
Given that p and q are the roots of the equation x2 – ax +b =0 and Dn= pn+qn. Find the value of Dn+1
Answer: Option A
:
A
Option (a)Shortcut: AssumptionAssume a quadratic equation. Let’s take x2+5x-6=0. Thus, a = sum of roots = -5 and b= product of roots = -6 Roots are p = 1 and q=-6D1= p1+q1 = -5D0 = 2D2 = 37Assume n=1We need to find Dn+1 = D2 = 37Look in the answer options for 37Option a is the only one which gives (-5)(-5)-(-6)(2) = 37
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:
A
Option (a)Shortcut: AssumptionAssume a quadratic equation. Let’s take x2+5x-6=0. Thus, a = sum of roots = -5 and b= product of roots = -6 Roots are p = 1 and q=-6D1= p1+q1 = -5D0 = 2D2 = 37Assume n=1We need to find Dn+1 = D2 = 37Look in the answer options for 37Option a is the only one which gives (-5)(-5)-(-6)(2) = 37
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