One of the five quadratics below has a repeated root. (There other four have distinct roots.) What is the repeated root? -x^2 + 18x + 81
3x^2 - 3x - 168
x^2 - 4x - 4
25x^2 - 30x + 9
x^2 - 14x + 24

3/5

Step-by-step explanation:

First one   18^2 - 4(-1)(81)  > 0    so no repeated root

Second one     (-3)^2  - 4(3) (-168)  >  0    so no repeated root

Third one   (-4) - (4) (1) (-4)  > 0      so no repeated root

Fourth one  (-30)^2  - 4(25) (9)   =  900 - 100(9)  =  0      repeated root

Note  this factors  as  (5x - 3)^2  

(5x - 3)^2  = 0     take both roots

5x - 3  = 0

5x  = 3

x  =  3/5   = repeated root

225x²+4=0

225x²=0-4

225x²=-4

x²=-4/225

x=±√-4/225

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