Solve 5i(2+4i)

$$5 i ( 2 + 4 i )$$

Evaluate

$$-20+10i$$

Solution Steps

Multiply 5i times 2+4i.

$$5i\times 2+5\times 4i^{2}$$

By definition, i^{2} is -1.

$$5i\times 2+5\times 4\left(-1\right)$$

Do the multiplications. Reorder the terms.

$$-20+10i$$

Real Part

$$-20$$

Solution Steps

Multiply 5i times 2+4i.

$$Re(5i\times 2+5\times 4i^{2})$$

By definition, i^{2} is -1.

$$Re(5i\times 2+5\times 4\left(-1\right))$$

Do the multiplications in 5i\times 2+5\times 4\left(-1\right). Reorder the terms.

$$Re(-20+10i)$$

The real part of -20+10i is -20.

$$-20$$