SOLUTION
Using the ratio of the parallel sides, we have
[tex]\frac{x+5}{12.8}=\frac{10}{x-3}[/tex]
Simplify by cross multiplying the fraction
[tex]\begin{gathered} (x+5)(x-3)=10\times12.8 \\ x^2-3x+5x-15=128 \\ x^2+2x-15-128=0 \\ x^2+2x-143=0 \end{gathered}[/tex]
The leads to a quadratic equation, which will be solved using the factor method
[tex]x^2+13x-11x-143=0[/tex]
By binomial factors, we have
[tex]\begin{gathered} x(x+13)-11(x+13)=0 \\ (x+13)(x-11)=0 \end{gathered}[/tex]
Then equate each expression to 0, we obtain
[tex]\begin{gathered} x+13=0\text{ 0r X-11=0} \\ x=-13,11 \end{gathered}[/tex]
Therefore x=-13,11
