Let Pn = n + n, n N. If P10 = 123, P9 = 76, P8 = 47 and P1 = 1, then the quadratic equation having roots 1 and 1 is :
- x2 + x - 1 = 0
- x2 - x + 1 = 0
- x2 + x + 1 = 0
- x2 - x - 1 = 0
Answer
(1) x2 + x - 1 = 0
Solution
+ = P1 = 1
P10 = ( + )P9 - P8 10 + 10 = ( + )( 9 + 9) - ( 8 + 8)
123 = 76 - 47 = -1
For roots 1 , 1 :
Sum = + = 1-1 = -1, Product = 1 = -1
x2 - (-1)x + (-1) = 0 x2 + x - 1 = 0
Answer: (1)