Note, first, that
i2 = -1; also, that
(1 + i)2 = 1 + 2i - 1 = 2i; and, finally, that
[±½(√2) ]2 = ½.
Thus, [±½(√2)(1 + i)]2 = i.
Therefore, [±½ (√2)(i - 1)]2 = -i, and
±½ (√2)(i - 1) = √-i.
* * *
In case calculus is familiar, you may prefer to find the desired roots in this manner:
eiθ = cosθ + i sinθ; thus, when
θ = ½ π, eiθ = i; and, when
θ = ¼ π, eiθ = +√i.
Then, +√i = cos ¼ π + i sin ¼ π
= (½√2) + i ½√2
= (½√2) (1 + i).
This gives,
+√-i = (+√i)(+√-1)
= i(+√i)
= (½√2) i(1 + i)
= (½√2) (i - 1).
Therefore the two roots are:
±√-i = ±(½√2)(i - 1).
* * *
The first method is simpler, for proving the result; the second method, for finding it.
Use a calculator (if you need) to find the principal square root. The second square root is the negative of the number.
Find the square root of 23. The second one is the same number with a negative sign.
√0.0256 = ± 0.16 The two square roots are 0.16 and -0.16.
The two square roots of i are (k, k) and (-k, -k) where k = sqrt(2)/2 = 1/sqrt(2).
256 has two square roots: 16 and -16.
Use a calculator (if you need) to find the principal square root. The second square root is the negative of the number.
Find the square root of 23. The second one is the same number with a negative sign.
√0.0256 = ± 0.16 The two square roots are 0.16 and -0.16.
The two square roots of i are (k, k) and (-k, -k) where k = sqrt(2)/2 = 1/sqrt(2).
The square roots of 196 are 14 and -14.
256 has two square roots: 16 and -16.
The two square roots of the number, '169', are +13 and -13 .
Both 9 and -9 are square roots of 81
The two square roots are +70 and -70 .
The two square roots of 18 are: 4.242641 and -4.242641
0.64 has square roots {0.8, -0.8}.
The two square roots are -22 and +22.