Question

for i= sqrt -1, if 3i(2+5i)=x+6i, then x=?

a. -15 b. 5 c. 5i d. 15i e. 27i

Answer 1

multiply like this
\[3i*2+5*3*i ^{2}\]
\[6i-15 (i ^{2}=-1)=x+6 i\]
now comparing lefthand and righthand side we get
x=-15

Answer 2

a -15 right ans.