Question 2.

The minimum possible value of x26x+103x\frac{x^2-6 x+10}{3-x}, for x<3, is

A
12\frac{1}{2}
B
12-\frac{1}{2}
C
2
D
-2

Question Explanation

Text Explanation

Let x26x+103x=p\frac{x^2 - 6x + 10}{3 - x} = p

x26x+10=3ppxx^2 - 6x + 10 = 3p - px

x2(6p)x+103p=0x^2 - (6 - p)x + 10 - 3p = 0

Since the equation will have real roots,

(6p)24×(103p)0(6 - p)^2 - 4 \times (10 - 3p) \ge 0

p212p+12p+36400p^2 - 12p + 12p + 36 - 40 \ge 0

p24p^2 \ge 4

p2, p2p \ge 2 ,\ p \le -2

Now, when p=2p = -2, x=4x = 4. Since it is given that x < 3, thus this value will be discarded.

Now, 12\frac{1}{2} and 12-\frac{1}{2} do not come in the mentioned range.

When p=2p = 2, x=2x = 2

Thus, the minimum possible value of p will be 2.

Thus, the correct option is C.

Alternate explanation:

Since x < 3,

3 - x > 0

Let 3x=y3 - x = y. So, y > 0.

Now,

x26x+103x=x26x+9+13x\frac{x^2 - 6x + 10}{3 - x} = \frac{x^2 - 6x + 9 + 1}{3 - x}

(3x)2+13x\Rightarrow \frac{(3 - x)^2 + 1}{3 - x}

Since 3x=y3 - x = y, the equation will transform to y2+1y\frac{y^2 + 1}{y} or y+1yy + \frac{1}{y}

The minimum value of the expression y+1yy + \frac{1}{y} for y > 0 will be at y=1y = 1

i.e. Minimum value = 1+1=21 + 1 = 2

Thus, the correct option is C.

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