Q.

If x is real show that value of the expression x2+34x71x2+2x7 does not lie between 5 and 9

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Detailed Solution

Let y=x2+34x71x2+2x7
yx2+2x7=x2+34x71yx2+2xy7y=x2+34x71 yx2+2xy7yx234x+71=0(y1)x2+2(y17)x+(7y+71)=0
Since xR , discriminent  0
{Compare with ax2+bx+c}
b24ac0.[2[y17]]24(y1)(7y+71)0[2(y17)]24(y1)(7y+71)04y234y+28947y2+78y7104y234y+289+7y278y+7108y2112y+3600;8y214y+450y214y+450;(y5)(y9)0y5 or y9
[If α<β then (xα)(xβ)0xα or xβ] y does not lie between 5 and 9

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If x is real show that value of the expression x2+34x−71x2+2x−7 does not lie between 5 and 9