Question

Can some one help please help me

Answer 1

Answer:

7

Explanation:

equation: x(x-2)=2x+21

find x:  $x^{2}$ -4x -21 = 0

(-b +/- $\sqrt{b^{2} - 4ac }$) /2a

(4 +/- $\sqrt{(-4)^{2} - 4(1)(-21)}$ ) /2(1)

(4 +/- 10) /2

= -3 and 7

-3 obviously does not work, but 7 does