First, you need to calculate the hypotenuse, this is possible because we know the value of one angle, 72 degrees, and one angle is 90 degrees.
sin72 = DC / AC , sin of an angle = opposite / hypotenuse
AC = DC / sin72, we must calculate the value of sin72 by calculator, and sin72 = 0,254
AC = 6/0,254 = 23,62
From here, we use the Pythagorean theorem to calculate AD, like such:
AD^2 = AC^2 - DC^2
AD^2 = 23,62^2 - 6^2
AD^2 = 557,90 - 36 = 521,9
AD = square root of 521,9
AD = 22,845 = 22,8
It seems a bit weird, but that's what the math says. Hope this helps!
