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jamesbob
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Two sides of a triangle have lengths a = 5cm and b = 10cm, and the included angle is [tex]\theta = \frac{\pi}{3}.[/tex] If a is increasing at a rate of 2cm/s, b is decreasing at a rate of 1cm/s and [tex]\theta[/tex] remains constant, at what rate os the third side changing? Is it increasing or decreasing?
Just wondering the best way to go about this question. I could calculate values of third side c after one second, then two etc, and figure out the rate of change. But we've been doing partial differentiation and differentials and so on. So do i say [tex] c^2 = a^2 + b^2 - 2ab\cos C [/tex] and take partial derivatives getting something like
[tex] (2a + 2b\cos C)da + (2b + 2a\cos C)db + (2ab\sin C)dc [/tex]
Then plug some form of values into that?
Just wondering the best way to go about this question. I could calculate values of third side c after one second, then two etc, and figure out the rate of change. But we've been doing partial differentiation and differentials and so on. So do i say [tex] c^2 = a^2 + b^2 - 2ab\cos C [/tex] and take partial derivatives getting something like
[tex] (2a + 2b\cos C)da + (2b + 2a\cos C)db + (2ab\sin C)dc [/tex]
Then plug some form of values into that?
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