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Derivative:f(x)=(cosx)^(cosx)

 

Find the derivative of the following via implicit differentiation: d/dx(f(x)) = d/dx(cos^(cos(x))(x)) The derivative of f(x) is f'(x): f'(x) = d/dx(cos^(cos(x))(x)) Express cos^(cos(x))(x) as a power of e: cos^(cos(x))(x) = e^(log(cos^(cos(x))(x))) = e^(cos(x) log(cos(x))): f'(x) = d/dx(e^(cos(x) log(cos(x)))) Using the chain rule, d/dx(e^(cos(x) log(cos(x)))) = ( de^u)/( du) ( du)/( dx), where u = cos(x) log(cos(x)) and ( d)/( du)(e^u) = e^u: f'(x) = d/dx(cos(x) log(cos(x))) e^(cos(x) log(cos(x))) Express e^(cos(x) log(cos(x))) as a power of cos(x): e^(cos(x) log(cos(x))) = e^(log(cos^(cos(x))(x))) = cos^(cos(x))(x): f'(x) = cos(x)^(cos(x)) d/dx(cos(x) log(cos(x))) Use the product rule, d/dx(u v) = v ( du)/( dx)+u ( dv)/( dx), where u = cos(x) and v = log(cos(x)): f'(x) = log(cos(x)) d/dx(cos(x))+cos(x) d/dx(log(cos(x))) cos^(cos(x))(x) The derivative of cos(x) is -sin(x): f'(x) = cos^(cos(x))(x) (cos(x) (d/dx(log(cos(x))))+-sin(x) log(cos(x))) Using the chain rule, d/dx(log(cos(x))) = ( dlog(u))/( du) ( du)/( dx), where u = cos(x) and ( d)/( du)(log(u)) = 1/u: f'(x) = cos^(cos(x))(x) (-(log(cos(x)) sin(x))+d/dx(cos(x)) sec(x) cos(x)) Simplify the expression: f'(x) = cos^(cos(x))(x) (d/dx(cos(x))-log(cos(x)) sin(x)) The derivative of cos(x) is -sin(x): f'(x) = cos^(cos(x))(x) (-(log(cos(x)) sin(x))+-sin(x)) Expand the left hand side: Answer: | | f'(x) = cos^(cos(x))(x) (-sin(x)-log(cos(x)) sin(x))

 

Derivative: 3y^3-4x^2y+xy=-5

 

Find the derivative of the following via implicit differentiation: d/dx(x y-4 x^2 y+3 y^3) = d/dx(-5) Differentiate the sum term by term and factor out constants: d/dx(x y)-4 d/dx(x^2 y)+3 d/dx(y^3) = d/dx(-5) Use the product rule, d/dx(u v) = v ( du)/( dx)+u ( dv)/( dx), where u = x and v = y: -4 (d/dx(x^2 y))+3 (d/dx(y^3))+x d/dx(y)+d/dx(x) y = d/dx(-5) Simplify the expression: x (d/dx(y))-4 (d/dx(x^2 y))+3 (d/dx(y^3))+(d/dx(x)) y = d/dx(-5) The derivative of y is y'(x): -4 (d/dx(x^2 y))+3 (d/dx(y^3))+y'(x) x+(d/dx(x)) y = d/dx(-5) Use the product rule, d/dx(u v) = v ( du)/( dx)+u ( dv)/( dx), where u = x^2 and v = y: 3 (d/dx(y^3))-4 x^2 d/dx(y)+d/dx(x^2) y+(d/dx(x)) y+x y'(x) = d/dx(-5) The derivative of y is y'(x): 3 (d/dx(y^3))+(d/dx(x)) y-4 (y'(x) x^2+(d/dx(x^2)) y)+x y'(x) = d/dx(-5) Using the chain rule, d/dx(y^3) = ( du^3)/( du) ( du)/( dx), where u = y and ( d)/( du)(u^3) = 3 u^2: 3 3 d/dx(y) y^2+(d/dx(x)) y+x y'(x)-4 ((d/dx(x^2)) y+x^2 y'(x)) = d/dx(-5) Simplify the expression: (d/dx(x)) y+9 (d/dx(y)) y^2+x y'(x)-4 ((d/dx(x^2)) y+x^2 y'(x)) = d/dx(-5) The derivative of y is y'(x): (d/dx(x)) y+y'(x) 9 y^2+x y'(x)-4 ((d/dx(x^2)) y+x^2 y'(x)) = d/dx(-5) The derivative of x is 1: 1 y+x y'(x)+9 y^2 y'(x)-4 ((d/dx(x^2)) y+x^2 y'(x)) = d/dx(-5) Use the power rule, d/dx(x^n) = n x^(n-1), where n = 2: d/dx(x^2) = 2 x: y+x y'(x)+9 y^2 y'(x)-4 (2 x y+x^2 y'(x)) = d/dx(-5) The derivative of -5 is zero: y+x y'(x)+9 y^2 y'(x)-4 (2 x y+x^2 y'(x)) = 0 Expand the left hand side: y-8 x y+x y'(x)-4 x^2 y'(x)+9 y^2 y'(x) = 0 Subtract y-8 x y from both sides: x y'(x)-4 x^2 y'(x)+9 y^2 y'(x) = -y+8 x y Collect the left hand side in terms of y'(x): (x-4 x^2+9 y^2) y'(x) = -y+8 x y Divide both sides by -4 x^2+x+9 y^2: Answer: | | y'(x) = (-y+8 x y)/(x-4 x^2+9 y^2)

 

y^3+sinhxy^2=3/2

 

Find the derivative of the following via implicit differentiation: d/dx(sinh^2(x y)+y^3) = d/dx(3/2) Differentiate the sum term by term: d/dx(sinh^2(x y))+d/dx(y^3) = d/dx(3/2) Using the chain rule, d/dx(sinh^2(x y)) = ( du^2)/( du) ( du)/( dx), where u = sinh(x y) and ( d)/( du)(u^2) = 2 u: d/dx(y^3)+2 d/dx(sinh(x y)) sinh(x y) = d/dx(3/2) Using the chain rule, d/dx(sinh(x y)) = ( dsinh(u))/( du) ( du)/( dx), where u = x y and ( d)/( du)(sinh(u)) = cosh(u): d/dx(y^3)+cosh(x y) d/dx(x y) 2 sinh(x y) = d/dx(3/2) Using the chain rule, d/dx(y^3) = ( du^3)/( du) ( du)/( dx), where u = y and ( d)/( du)(u^3) = 3 u^2: 2 cosh(x y) (d/dx(x y)) sinh(x y)+3 d/dx(y) y^2 = d/dx(3/2) The derivative of y is y'(x): 2 cosh(x y) (d/dx(x y)) sinh(x y)+y'(x) 3 y^2 = d/dx(3/2) Use the product rule, d/dx(u v) = v ( du)/( dx)+u ( dv)/( dx), where u = x and v = y: x d/dx(y)+d/dx(x) y 2 cosh(x y) sinh(x y)+3 y^2 y'(x) = d/dx(3/2) The derivative of y is y'(x): 2 cosh(x y) sinh(x y) (y'(x) x+(d/dx(x)) y)+3 y^2 y'(x) = d/dx(3/2) The derivative of x is 1: 3 y^2 y'(x)+2 cosh(x y) sinh(x y) (1 y+x y'(x)) = d/dx(3/2) The derivative of 3/2 is zero: 3 y^2 y'(x)+2 cosh(x y) sinh(x y) (y+x y'(x)) = 0 Expand the left hand side: 2 cosh(x y) sinh(x y) y+2 x cosh(x y) sinh(x y) y'(x)+3 y^2 y'(x) = 0 Subtract 2 y sinh(x y) cosh(x y) from both sides: 2 x cosh(x y) sinh(x y) y'(x)+3 y^2 y'(x) = -2 cosh(x y) sinh(x y) y Collect the left hand side in terms of y'(x): (2 x cosh(x y) sinh(x y)+3 y^2) y'(x) = -2 cosh(x y) sinh(x y) y Divide both sides by 2 x sinh(x y) cosh(x y)+3 y^2: Answer: | | y'(x) = -(2 cosh(x y) sinh(x y) y)/(2 x cosh(x y) sinh(x y)+3 y^2)

 

Let y=sin(n*sin^-1x), n>0.Show that: (1 - x^2)*y" - xy' + n^2y=0

 

n>0,   y = sin(n sin^(-1)(x))

 

P.S. YOU HAVE TO RE-SUBMIT THE LAST TWO IN HAND-WRITING. DO NOT USE A MATH PACKAGE SUCH AS LA TEX.....ETC., BECAUSE WE CANNOT COPY AND PASTE THEM!.

Feb 10, 2016
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Feb 10, 2016
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Feb 10, 2016
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lim x-->9 (x sqrt(3) - 3) / (x - 9)

 

(two-sided limit does not exist)

lim_(x->9^-) (x sqrt(3)-3)/(x-9) = -infinity (Limit from the left)

lim_(x->9^+) (x sqrt(3)-3)/(x-9) = infinity (limit from the right)

 

lim x-->∞ (3 + 2/x) * cos(1/x)

 

Find the following limit:

lim_(x->infinity) cos(1/x) (3+2/x)

Applying the product rule, write lim_(x->infinity) (3+2/x) cos(1/x) as (lim_(x->infinity) (3+2/x)) (lim_(x->infinity) cos(1/x)):

lim_(x->infinity) (3+2/x) lim_(x->infinity) cos(1/x)

Using the fact that cosine is a continuous function, write lim_(x->infinity) cos(1/x) as cos(lim_(x->infinity) 1/x):

lim_(x->infinity) (3+2/x) cos(lim_(x->infinity) 1/x)

Let epsilon>0. Then for all x > 1/epsilon, 1/x<1/(1/epsilon) = epsilon, so

lim_(x->infinity) 1/x = 0:

cos(0) lim_(x->infinity) (3+2/x)

cos(0) = 1:

lim_(x->infinity) (3+2/x)

3+2/x = lim_(x->infinity) 3+2 (lim_(x->infinity) 1/x):

lim_(x->infinity) 3+2 lim_(x->infinity) 1/x

Let epsilon>0. Then for all x > 1/epsilon, 1/x<1/(1/epsilon) = epsilon, so

lim_(x->infinity) 1/x = 0:

lim_(x->infinity) 3+2×0

Since 3 is constant, lim_(x->infinity) 3 = 3:

3+2×0

3+2 0 = 3:

Answer: |=3

 

lim x-->0 ((1 -  cos(ax)) / x^2)

 

Find the following limit: lim_(x->0) (1-cos(a x))/x^2 Applying l'Hôpital's rule, we get that lim_(x->0) (1-cos(a x))/x^2 = lim_(x->0) ( d/( dx)(1-cos(a x)))/( d/( dx) x^2) = lim_(x->0) (a sin(a x))/(2 x) lim_(x->0) (a sin(a x))/(2 x) (a lim_(x->0) (sin(a x))/x)/(2) Applying l'Hôpital's rule, we get that lim_(x->0) (sin(a x))/x | = | lim_(x->0) ( d/( dx) sin(a x))/(( dx)/( dx)) | = | lim_(x->0) (a cos(a x))/1 | = | lim_(x->0) a cos(a x) (a lim_(x->0) a cos(a x))/2 lim_(x->0) a cos(a x) = a cos(0 a) = a: (a a)/2 1/2 a a = a^2/2: Answer: | | a^2/2

 

lim x-->∞ (x^1/3 - 5x + 3) / (2x + x^2/3 - 4)

 

Find the following limit: lim_(x->infinity) (3+x^(1/3)-5 x)/(x^2/3+2 x-4) (3+x^(1/3)-5 x)/(x^2/3+2 x-4) = (3+x^(1/3)-5 x)/(x^2/3+2 x-4): lim_(x->infinity) (3+x^(1/3)-5 x)/(x^2/3+2 x-4) The leading term in the denominator of (3+x^(1/3)-5 x)/(x^2/3+2 x-4) is x^2. Divide the numerator and denominator by this: lim_(x->infinity) (3/x^2+1/x^(5/3)-5/x)/(1/3+2/x-4/x^2) The expressions 3/x^2, 1/x^(5/3), -5/x, -4/x^2 and 2/x all tend to zero as x approaches infinity: 0/(1/3) 0/(1/3) = 0: Answer: | | 0

 

lim x-->∞ (sqrt(x^2 + x)) - sqrt(x^2 - cx), c=positive constant

 

You didn't specify the limit:lim_(x->infinity) (sqrt(x^2+x)-sqrt(x^2-c x)) = (1+c)/2

Feb 10, 2016

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