Evaluate
21+9i
Real Part
21
Share
Copied to clipboard
3\times 5+3\times \left(-2i\right)+3i\times 5+3\left(-2\right)i^{2}
Multiply complex numbers 3+3i and 5-2i like you multiply binomials.
3\times 5+3\times \left(-2i\right)+3i\times 5+3\left(-2\right)\left(-1\right)
By definition, i^{2} is -1.
15-6i+15i+6
Do the multiplications.
15+6+\left(-6+15\right)i
Combine the real and imaginary parts.
21+9i
Do the additions.
Re(3\times 5+3\times \left(-2i\right)+3i\times 5+3\left(-2\right)i^{2})
Multiply complex numbers 3+3i and 5-2i like you multiply binomials.
Re(3\times 5+3\times \left(-2i\right)+3i\times 5+3\left(-2\right)\left(-1\right))
By definition, i^{2} is -1.
Re(15-6i+15i+6)
Do the multiplications in 3\times 5+3\times \left(-2i\right)+3i\times 5+3\left(-2\right)\left(-1\right).
Re(15+6+\left(-6+15\right)i)
Combine the real and imaginary parts in 15-6i+15i+6.
Re(21+9i)
Do the additions in 15+6+\left(-6+15\right)i.
21
The real part of 21+9i is 21.
Examples
Quadratic equation
{ x } ^ { 2 } - 4 x - 5 = 0
Trigonometry
4 \sin \theta \cos \theta = 2 \sin \theta
Linear equation
y = 3x + 4
Arithmetic
699 * 533
Matrix
\left[ \begin{array} { l l } { 2 } & { 3 } \\ { 5 } & { 4 } \end{array} \right] \left[ \begin{array} { l l l } { 2 } & { 0 } & { 3 } \\ { -1 } & { 1 } & { 5 } \end{array} \right]
Simultaneous equation
\left. \begin{cases} { 8x+2y = 46 } \\ { 7x+3y = 47 } \end{cases} \right.
Differentiation
\frac { d } { d x } \frac { ( 3 x ^ { 2 } - 2 ) } { ( x - 5 ) }
Integration
\int _ { 0 } ^ { 1 } x e ^ { - x ^ { 2 } } d x
Limits
\lim _{x \rightarrow-3} \frac{x^{2}-9}{x^{2}+2 x-3}