square root of -1=i 2i(2+5i)=x+6i x=? i keep coming up with 15i the answer is -15 what am i doing wrong? what formula should i use to solve
$$\begin{array}{rlll} -2i(2+5i)&=&x+6i\\ -4i-10i^2&=&x+6i\\ -4i+10&=&x+6i\\ -10i+10&=&x\\ x&=&10-10i\\ \end{array}$$
