Question

What is the value of X?

Answer 1

∆ABC similar to ∆CBD

DB/AC = CB/AB

$\frac{x}{7.5} = \frac{7.5}{x + 3} \\ x(x + 3) = {7.5}^{2} = { (\frac{15}{2}) }^{2} \\ {x}^{2} + 3x = \frac{225}{4} \\ 4 {x}^{2} + 12x = 225 \\ 4 {x}^{2} + 12x + 9 = 216 \\ {(2x + 3)}^{2} = 216 \\ 2x + 3 = 6 \sqrt{6} \\ x = - 1.5 + 3 \sqrt{6}$

approximately 6.1485