Maxima and minima (trapezoidal gutter)
I have a problem sir.
h=1/2√4a^2-(b-a)^2
A=1/4(b+a)√4a^2-(b-a)^2
dA/db=1/4[(b+a)-2(b-a)/2√4a^2-(b-a)^2 + √4a^2-(b-a)^2]=0.
Question:
How did it become +√4a^2-(b-a)^2]=0?
How did it become zero? Why is there zero?