Check My Math Answers - Is It Right or Wrong?

[buffgilville]

I done these problems, can anyone tell me if it's right or wrong? Thanks

1) Compute lim (as x approaches 2) of (3x sin(pi x) + cos (pi x))
I got: 1

2) Use the derivative rule to find 1/(x-4)
I got: -1/((x+h-4)(x-4))

3) Find an equation for the tangent line to the graph given by:
2x^2 + xy - 4y^2 = 2
at the point where (x,y) = (2, -1)

I got: y = -(7/10)x + (2/5)

4) A 5 foot girl is walking towards a 24 foot lamppost at the rate of 7 feet per second. At what speed is the tip of her shadow moving when she is 8 feet from the lampost?
I got: (168/19) feet per second

 

[marlon]

first three questions seem ok to me.
The second answer is the limit for h to zero of your solution devided by h. Ofcourse if you just apply the standard rules you get : -1/(x-4)²

marlon
i don't get your fourth question though...

 

[Tide]

Buff,

I got the same number you did for problem 4 on my first pass.

 

[marlon]

hi Buff,

Yes, yes, yes, got the same answer for question four...

marlon