Question

Find the length of the curve. R(t) = 7t, 3 cos(t), 3 sin(t) , −2 ≤ t ≤ 2

Answer 1

we are given

$r(t)=(7t,3cos(t),3sin(t))$

we can find x , y and z

$x=7t,y=3cos(t),z=3sin(t))$

now, we can use arc length formula

$L=\int\limits^a_b {\sqrt{(x')^2+(y')^2+(z')^2} } \, dt$

now, we can find derivative

$x'=7,y'=-3sin(t),z'=3cos(t))$

now, we can plug values

and we get

$L=\int _{-2}^2\sqrt{7^2+\left(-3\sin \left(t\right)\right)^2+\left(3\cos \left(t\right)\right)^2}dt$

$L=\int _{-2}^2\sqrt{7^2+9}dt$

$=\sqrt{58}\cdot \:2-\left(-2\sqrt{58}\right)$

$L=4\sqrt{58}$...........Answer