document.write( "Question 1118792: Find b if f(x)= x^2-bx+9 has one rational root and b >0. \n" ); document.write( "

Algebra.Com's Answer #734223 by ikleyn(52864) $\"\"$ $\"About$

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document.write( "f(x) = x^2 - bx + 9.\r\n" );
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document.write( "f(x) has one rational root if and only if the discriminant of this quadratic equation is zero\r\n" );
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document.write( "d = (-b)^2 - 4*1*9 = 0,   or   b^2 - 36 = 0,\r\n" );
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document.write( "which implies  b = +/-6.\r\n" );
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document.write( "Since the problem requires  b > 0,  there is only one solution  b = 6.\r\n" );
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