Let r be a root of the equation π₯^2 + 2π₯ + 6 = 0. Then the value of theβ¦
2022
Let r be a root of the equation π₯^2 + 2π₯ + 6 = 0.
Then the value of the expression (π + 2)(π + 3)(π + 4)(π + 5) is
- A.
51
- B.
-51
- C.
126
- D.
-126
Attempted by 32 students.
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Correct answer: D
We need the value of (r + 2)(r + 3)(r + 4)(r + 5) where r satisfies r^2 + 2r + 6 = 0.
Use the equation to express r^2 in terms of r: r^2 = -2r - 6.
Pair the factors: (r + 2)(r + 5) = r^2 + 7r + 10 = (β2r β 6) + 7r + 10 = 5r + 4.
Similarly, (r + 3)(r + 4) = r^2 + 7r + 12 = (β2r β 6) + 7r + 12 = 5r + 6.
Multiply the two results: (5r + 4)(5r + 6) = 25r^2 + 50r + 24. Substitute r^2 = β2r β 6:
25(β2r β 6) + 50r + 24 = β50r β 150 + 50r + 24 = β126.
Final answer: -126
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