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