Explanation:
there is no real number solution for the square root of a negative number.
a sqare root multiplied by itself had to deliver exactly the number inside the square root.
so for sqrt(-49), what can be the answer ?
which number multiplied by itself gives -49 ?
it any negative number at that.
because
a × a = a²
and
-a × -a = a² but definitely not -a².
we get a negative number only, when we multiply a positive number with a negative number or vice versa.
the only solution is complex or imaginary (based on the imaginary number i):
i² = -1
i = sqrt(-1)
so, sqrt(-49) = sqrt(49 × -1) = 7×sqrt(-1) = 7i
but again, no real solution.