Answer:
7
Explanation:
equation: x(x-2)=2x+21
find x: [tex]x^{2}[/tex] -4x -21 = 0
(-b +/- [tex]\sqrt{b^{2} - 4ac }[/tex]) /2a
(4 +/- [tex]\sqrt{(-4)^{2} - 4(1)(-21)}[/tex] ) /2(1)
(4 +/- 10) /2
= -3 and 7
-3 obviously does not work, but 7 does
