# What does 'li' mean?

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Mohiedin Bagheri on 20 Oct 2021
Edited: James Tursa on 20 Oct 2021
Hello all,
I have solved an equation in matlab using the following code:
syms x
ththa2 = (2*exp(5*x))/(3*exp(2*x)+1*exp(-2*x))
y = diff(ththa2)
eqn = y == 0
S = solve(eqn)
S =
log(-(7^(1/2)*1i)/3)/2
log((7^(1/2)*1i)/3)/2
Would you please tell me what does this '1i' mean in the answer? What kind of a value is this?
Thank you,
Mohi

KSSV on 20 Oct 2021
Edited: KSSV on 20 Oct 2021
1i stands for complex number. i.e. sqrt(-1).
c=2+3*i
c = 2.0000 + 3.0000i
c=2+3*1i
c = 2.0000 + 3.0000i

Image Analyst on 20 Oct 2021
It's i, the square root of -1, the imaginary constant.

James Tursa on 20 Oct 2021
Edited: James Tursa on 20 Oct 2021
1i is used to ensure it isn't confused with a variable named i that you might have in the workspace. I.e., 1i is always sqrt(-1), whereas just i might be sqrt(-1) or a variable that you created named i. It is common to see 1i used in MATLAB for sqrt(-1) because it is always unambiguous.