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hey can you all help me with some Calculus problems:

1. find dy/dx if y=sin(x+y)
a. o
b. cos(x+y)/1-cos(x+y)
c. cos(x+y)
d. 1
e. None of these

4. find dy/dx for 7x^2 +6xy+9y^2=0
a. -7x+3y/9y
b. -7x+3y/3x+9y
c. 7x+9y/-3x
d. 14x+6y+18y
e. None of these

Thank you so much!!!! Can you show me your work so that I can see what i am doing wrong

By Screwed4life (Screwed4life) on Tuesday, October 14, 2003 - 08:32 pm: Edit

BUMP

By Screwed4life (Screwed4life) on Tuesday, October 14, 2003 - 09:20 pm: Edit

BUMP Please someone help me! LOL

By Fofisty (Fofisty) on Tuesday, October 14, 2003 - 09:25 pm: Edit

1. c

By Fofisty (Fofisty) on Tuesday, October 14, 2003 - 09:30 pm: Edit

4. d - f(x)= 7x^2+6xy+9^2
f'(x)=(2*7)x+(1*6)y+(2*9)y
f'(x)= 14x + 6y + 18y

By Screwed4life (Screwed4life) on Tuesday, October 14, 2003 - 09:50 pm: Edit

Thanks but how did you get C for number one..can you please show me your work

And on 4 shouldn't the derivative of 9y^2 be 18y(dy/dx)

By Mew24680 (Mew24680) on Tuesday, October 14, 2003 - 10:08 pm: Edit

it cant be c, too easy of an answer, u need to factor in the y.

By Rohan_Gokhale (Rohan_Gokhale) on Wednesday, October 15, 2003 - 02:48 pm: Edit

y=sin(x+y)
diff w.r.t x
dy\dx = d\dx sin(x+y) *d\dx(x+y)
= cos(x+y) *dx\dx+dy\dx
= cos(x+y) *(1+dy\dx)
dy\dx = cos(x+y) + cos(x+y)*dy+dx
dy\dx - cos(x+y)*dy\dx = cos(x+y)
dy\dx (1 - cos(x+y) = cos(x+y)
therefore dy\dx = cos(x+y)\ 1 - cos(x+y)
the answer is B