1.The base of an isosceles triangle is 20cm and the altitude is increasing at the rate of 1cm/min. At what rate is the base angle increasing when the area is 100cm^2?

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- August 29th 2008, 10:45 AMmatthewspjTrigonometric differentiation problem
1.The base of an isosceles triangle is 20cm and the altitude is increasing at the rate of 1cm/min. At what rate is the base angle increasing when the area is 100cm^2?

- August 29th 2008, 11:49 AMJhevon
A is the area, h is the height, b is the length of the base and is the base angle.

recall that

this means, when A = 100, h = 10.

we are also told that . b is constant at 20cm, and so , but we wont even have to worry about that.

draw your triangle, and bisect the base with a vertical line going through the top vertice. is the base angle and we form a right triangle with the opposite side to theta being h and the adjacent side being 10.

Thus we have

now differentiate implicitly and continue