Thread: From Altitudes to Angle to Sides

I dont know where to start

Altitude -- from Wolfram MathWorld

In most cases the altitude of the triangle is inside the triangle, like that image example

AB = c, BC = a, AC = b

24 b = 56 c = 21 a = twice area ABC

solve for b, c in terms of a and replace in

$\displaystyle a^2+c^2-2 a c \cos B=b^2$

we get

$\displaystyle \cos B=1/2$