1.

The value of `b`for which the equation `2(log)_(1/(25))(b x+28)=-(log)_5(12-4x-x^2)`has coincident roots is`b=-12`(b) `b=4orb=-12``b=4orb=-12`(d)`b=-4orb=12`

Answer» LHS
`2log_(1/25)(bx+28)2log_(5^(-2))(bx+28)`
LHS
`(2/-2)log_5(bx+28)=-log_5(bx+28)`
`log_5(bx+28)=-log_5(12-4x-x^2)`
`log_a^x=log_a^y`
`x=y`
`bx+28=12-4x-x^2`
`x^2+4x+bx+28-12=0`
`x^2+(4+b)x+16=0`
`(4+b)^2-4*16=0`
`16+b^2+8b-64=0`
`b^2+8b-48=0`
`(b+12)(b-4)=0`
`b=4,-12`.


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