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Question: The expression \(\frac{x^{2} + 2x + 1}{x^{2} + 2x + 7}\) lies in the interval (x Ī R)...

The expression x2+2x+1x2+2x+7\frac{x^{2} + 2x + 1}{x^{2} + 2x + 7} lies in the interval (x Ī R)

A

[0, – 1]

B

(–, 1) Č [1, )

C

[0, 1)

D

None of these

Answer

[0, 1)

Explanation

Solution

Let y = x2+2x + 1/x 2 + 2x + 7

Ž x2(1– y) + 2x (1–y)+1–7y = 0, As x is real, so D ³ 0;

i.e. 4(1 – y)2 – 4(1 – y) (1 – 7y) ³ 0;

1 + y2–2y–7y2 + 8y – 1 ³ 0

Ž – 6y2 + 6y ³ 0 = y2 – y £ 0

\ y Ī [0, 1) (As y ¹ 1)