Calc

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I get part i) and ii), but part iii)b) fucked me over.
Here's apparently what the solution is.

I really don't understand how he went from line 3 to line 4. How did he know they were 0? and how did he know it was axb?

>>8525284
Wow OP for a moment I stared at your pic and couldn't figure out how to solve the first exercises, I got desperate and felt like shit, it was really painful. But then I re-read and figured out I had read it wrong or idk, the point is that I figured out I can solve them effortlessly, thank god I'm not a brainlet, cheers op.

>>8525353
Nice one. Could you explain the last one to a brainlet like me - in particular, how he gets the 0s and the axb?

>>8525284
Look up the definition for gradient and then you should be able to bool.

http://tutorial.math.lamar.edu/Classes/CalcIII/GradientVectorTangentPlane.aspx

Don't have much time to help m8, I need to study for a small exam today.

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>>8525284

This is almost high school level crap. How /sci/ has fallen.

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>>8525407
No? What high school did you go to faggot?

>>8525407
idk, I'm in year 2 glasgow uni doing physics. If this is highschool crap then the standard of the world has skyrocketed in the last few years without anybody noticing. Or you're a savant.

>>8525407
Multivariable calculus in HS? Must be a murica thing pal

>>8525284
tensors are your friend bro

none of you are helping ;_;

This is Calc I now?

bump. Need to understand. Exam's tomorrow.

>>8525289
Curl(b) is zero because b is constant.
Same for grad(a.b), a is also constant.
Apply the definition of curl to r=(x,y,z) and you will see why it is also zero.
If you say a=(a1,a2,a3) then a.r=a1x+a2y+a3z.
Then from the definition of the gradient, grad(a.r)=a

Hope this helps.

>>8525685
THANK YOU <3333