[tex]\bf (-4i)(7i)\implies -28i^2\implies \stackrel{\textit{recall that }i^2 = -1}{-28(-1)}\implies 28[/tex]
For this case we must simplify the following expression:
[tex](-4i) (7i)[/tex]
We have to by definition that:
[tex]- * + = -\\- * - = +\\i ^ 2 = -1[/tex]
So:
[tex]-4i * 7i = -28i ^ 2 = -28 (-1) = 28[/tex]
Finally we have that the expression is equivalent to:
[tex](-4i) (7i) = 28[/tex]
Answer:
[tex](-4i) (7i) = 28[/tex]
