Question

the base of an isosceles triangle is 10 ft long and the base angles are decreasing at a rate of 2 degree per secnd. find the rate of change of the area when the base angles are 45 degree

Answer 1

We have the height h is 

h = 5tanθ 

a = 5h = 25tanθ 
da/dt = 25sec^2θ dθ/dt 

Now just plug in your numbers (in radians!)