Evaluate
7+21i
Real Part
7
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7i\times 3+7\left(-1\right)i^{2}
Multiply 7i times 3-i.
7i\times 3+7\left(-1\right)\left(-1\right)
By definition, i^{2} is -1.
7+21i
Do the multiplications. Reorder the terms.
Re(7i\times 3+7\left(-1\right)i^{2})
Multiply 7i times 3-i.
Re(7i\times 3+7\left(-1\right)\left(-1\right))
By definition, i^{2} is -1.
Re(7+21i)
Do the multiplications in 7i\times 3+7\left(-1\right)\left(-1\right). Reorder the terms.
7
The real part of 7+21i is 7.
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