Let the base = x
Then the height would be 2x ( twice the length of the base.
Now using the given formula you get:
25 = 1/2 * 2x *x
Multiply 2x by 1/2:
1/2 * 2x = 2x/2
25 = 2x/2 * x
2x/2 = 1x, now you have:
25 = x *x
Multiply x by x:
25 = x^2
Take the square root of both sides:
x = √25
x = 5