Thursday 10 November 2016

`x=sqrt(t) , y=3t-1 , 0

Arc length of a curve C described by the parametric equations x=f(t) and y=g(t),`a<=t<=b` , where f'(t) and g'(t) are continuous on [a,b] and C is traversed exactly once as t increases from a to b , then the length of the curve C is given by:


`L=int_a^bsqrt((dx/dt)^2+(dy/dt)^2)dt`


Given parametric equations are :`x=sqrt(t),y=(3t-1) , 0<=t<=1`


`x=sqrt(t)`


`=>dx/dt=1/2(t)^(1/2-1)`


`dx/dt=1/2t^(-1/2)`


`dx/dt=1/(2sqrt(t))`


`y=3t-1`


`dy/dt=3`


Now let's evaluate the length of the arc by using the stated formula,


`L=int_0^1sqrt((1/(2sqrt(t)))^2+3^2)dt`


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Arc length of a curve C described by the parametric equations x=f(t) and y=g(t),`a<=t<=b` , where f'(t) and g'(t) are continuous on [a,b] and C is traversed exactly once as t increases from a to b , then the length of the curve C is given by:


`L=int_a^bsqrt((dx/dt)^2+(dy/dt)^2)dt`


Given parametric equations are :`x=sqrt(t),y=(3t-1) , 0<=t<=1`


`x=sqrt(t)`


`=>dx/dt=1/2(t)^(1/2-1)`


`dx/dt=1/2t^(-1/2)`


`dx/dt=1/(2sqrt(t))`


`y=3t-1`


`dy/dt=3`


Now let's evaluate the length of the arc by using the stated formula,


`L=int_0^1sqrt((1/(2sqrt(t)))^2+3^2)dt`


`L=int_0^1sqrt(1/(4t)+9)dt`


`L=int_0^1sqrt((1+36t)/(4t))dt`


`L=int_0^1sqrt(1+36t)/sqrt(4t)dt`


`L=int_0^1 1/2sqrt(1+36t)/sqrt(t)dt`


Take the constant out,


`L=1/2int_0^1sqrt(1+36t)/sqrt(t)dt`


Let's first evaluate the indefinite integral:`intsqrt(1+36t)/sqrt(t)dt`


Use integral substitution:`u=6sqrt(t)`


`du=6(1/2)t^(1/2-1)dt`


`du=3/sqrt(t)dt`


`intsqrt(1+36t)/sqrt(t)dt=int1/3sqrt(1+u^2)du`


`=1/3intsqrt(1+u^2)du`


Use the following standard integral from the integration tables:


`intsqrt(u^2+a^2)du=1/2(usqrt(u^2+a^2)+a^2ln|u+sqrt(a^2+u^2)|)+C`


`=1/3[1/2(usqrt(u^2+1)+ln|u+sqrt(1+u^2)|)]+C`


`=1/6(usqrt(1+u^2)+ln|u+sqrt(1+u^2)|)+C`


Substitute back:`u=6sqrt(t)`


`=1/6(6sqrt(t)sqrt(1+36t)+ln|6sqrt(t)+sqrt(1+36t)|)+C`


`L=1/2[1/6(6sqrt(t)sqrt(1+36t)+ln|6sqrt(t)+sqrt(1+36t)|)]_0^1`


`L=1/12[6sqrt(t)sqrt(1+36t)+ln|6sqrt(t)+sqrt(1+36t)|]_0^1`


`L=1/12{[6sqrt(37)+ln|6+sqrt(37)|]-[ln|1|]}`


`L=1/12[6sqrt(37)+ln|6+sqrt(37)|]`


Using calculator,


`L=1/12[36.4965751818+ln12.0827625303]`


`L=1/12[38.9883550344]`


`L=3.2490295862`


`L~~3.249`


Arc length of the curve on the given interval `~~3.249`


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