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The quadratic equation $2x^2 + bx + 18 = 0$ has a double root. Find all possible values of $b.$

 Jan 24, 2021
 #1
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Complete the square, to get 2(x + 3)^2 = 2x^2 + 6x + 18 ==> b = 6.

 Jan 24, 2021
 #2
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If we have a double root.....the discriminant  =   0

 

So

 

b^2   - 4 *2 * 18   =  0

 

b^2  -144   =  0

 

b^2   =  144

 

b  =  12    or   b   = -12

 

 

cool cool cool

 Jan 24, 2021

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