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\left(3+4i\right)z=5
The modulus of a complex number a+bi is \sqrt{a^{2}+b^{2}}. The modulus of 4+3i is 5.
z=\frac{5}{3+4i}
Divide both sides by 3+4i.
z=\frac{5\left(3-4i\right)}{\left(3+4i\right)\left(3-4i\right)}
Multiply both numerator and denominator of \frac{5}{3+4i} by the complex conjugate of the denominator, 3-4i.
z=\frac{5\left(3-4i\right)}{3^{2}-4^{2}i^{2}}
Multiplication can be transformed into difference of squares using the rule: \left(a-b\right)\left(a+b\right)=a^{2}-b^{2}.
z=\frac{5\left(3-4i\right)}{25}
By definition, i^{2} is -1. Calculate the denominator.
z=\frac{5\times 3+5\times \left(-4i\right)}{25}
Multiply 5 times 3-4i.
z=\frac{15-20i}{25}
Do the multiplications in 5\times 3+5\times \left(-4i\right).
z=\frac{3}{5}-\frac{4}{5}i
Divide 15-20i by 25 to get \frac{3}{5}-\frac{4}{5}i.