Question

Find ds/dt for s=cos^4(1-2t). I wanna know the working. The answer is 8cos^3 (1-2t) sin(1-2t)

Answer 1

Omg help

Answer 2

You have to use the Chain Rule. Logic tells you that it should be \[ \dfrac {4}{3} \cos^3 (1 - 2t) \](That is how you would differentiate x^4.) But, the chain rule puts 4(-2)(sin(1-2t)). To see why, you have to learn the Chain Rule. Do you know about it?

Answer 3

Yes I know about the chain rule but how to apply it. The power is 4. :|

Answer 4

Okay. You have to multiply power * derivative of argument (derivative of 1-2t, that is) * - sin (1-2t). The - sin (1-2t) comes from the fact that the derivative of cosine is - sine.

Answer 5

Isn't it supposed to be 4 cos^3(1-2t)

Answer 6

Oh haha I'll try to understand that

Answer 7

You forgot the - sin (1-2t) part. Remember that you have to incorporate the part where you find the derivative of the original and substitute the argument.

Answer 8

Thanks! Now I get it.

Answer 9

You're welcome! I'm glad I could help. :)

Answer 10

Me too! I will try to figure that part out :)