Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[bahihs]

Can someone please help me with the stat question I posted? The test in two days and I'm getting worried.

[Spehss _]

Can someone please help me with the stat question I posted? The test in two days and I'm getting worried.

I'd help if I was familiar with statistics. That's "stat", right?

[Reelya]

Am I doing things right? And where did the dy/dx come from between steps 2 and 3 in part A? I don't give a shit how efficiently I could've done it or what other methods there are to solve the problem, I want to know if I'm doing the "implicit differentiations" shit right.

The added dy/dx was needed because the differential where (y^2) = 2y is actually y^2 differentiated with respect to y, not x. So I'm guessing it's actually d(y^2)/dy * dy/dx to cast it into a differential with respect to x, not y. Note that there are a dy on the top and bottom, which "cancel out" according to the slightly arcane rules of calculus.

[Spehss _]

The added dy/dx was needed because the differential where (y^2) = 2y is actually y^2 differentiated with respect to y, not x. So I'm guessing it's actually d(y^2)/dy * dy/dx to cast it into a differential with respect to x, not y. Note that there are a dy on the top and bottom, which "cancel out" according to the slightly arcane rules of calculus.

If it was d(y^2)/dy, wouldn't the result just be 2, not 2y? d(x)/dx is just 1, for example.

[Reelya]

but it's y-squared not y.

[Spehss _]

but it's y-squared not y.

...Right. 2y is not y^2. Probably should've thought more before posting that.

[MagmaMcFry]

Spehss_?
Please stop scaring me.

Spoiler: *eldritch noises* (click to show/hide)

Yes, this is actually maths. I actually need to condense half a book's worth of this stuff into a bachelor's thesis.

[bahihs]

Can someone please help me with the stat question I posted? The test in two days and I'm getting worried.

I'd help if I was familiar with statistics. That's "stat", right?

Indeed it is, Bayesian Statistics to be specific

[Spehss _]

Assuming I did this right, solving for dy/dx using implicit differentiation for x^(3)+y^(3)=1 then y'=(-3x^(2))/(3y^(2)).

Right? This seems way simpler than the example I worked through yesterday. Makes me think I'm doing it wrong.

[Arx]

Insofar as the forum makes it easy to read, I believe you are correct.

x³+y³ = 1
∴ y' = (3x²)/(3y²)

Yes?

Pseudoedit: Also what Ispil said. Markers tend to be anal about simplification at this level of calc.

[Spehss _]

So I'm still not sure where y' fits in when solving implicit differentiations.

Working out one problem. Find y' of x²y²+xsiny=4.

I've found the derivatives of both sides of the equation, so it's currently 2x²y+2xy²+xcosy+siny=0. So now I solve for y'. But I'm not sure where y' is supposed to be included in that equation. Before this problem I figured y' would be multiplied with the y variable, and all the past problems worked out fine. But in this case that doesn't work because there's multiple instances of y variables.

[Arx]

It's the same as before, you just have to do the same thing for every instance of y (so, 2(x²y)dy/dx etc).

[Spehss _]

Every time you take the derivative of y itself, multiply by a y' (think about it; you took the derivative of y, which is y', so multiply by y' to show this). Then get everything that doesn't have y' on the right side, everything with a y' on the left side, factor out y', and divide.

So it'd be 2x²y(y')+2xy²+xcosy(y')+siny=0 because of using y' in the derivative of x²y² and using y' in the derivative of sin(y)?

[Arx]

That looks right, assuming your trig derivatives are all kosher (which appears to be the case).

[frostshotgg]

Pseudoedit: Also what Ispil said. Markers tend to be anal about simplification at this level of calc.

My experience is the opposite. Once you get to calculus, it's all about the process, not about algebra. Usually if your answer is an unsimplified form, they'll accept it. The answer is only 1 point anyways.