High School Mathematics Questions and Answers. Feel free to use the Search bar for this site, just below. The list of Labels in the right hand column below is also useful.
Most of the questions on this site are from NSW, Australia curriculum.
QUESTION: Vectors : Arc length of a space curve Use the integration capabilities of you graphing utility to approximate the arc length of the space curve given by: vector $$r(t) = t i + t^3 j + 3k$$ from the point $(1,1,3)$ to the point $(2,8,6)$. Round your answer to the nearest three decimal places.
SOLUTION ======================= Theory. If you have a curve $r(t) = x(t) i + y(t) j + z(t) k$ then the arc length between two points where t=a to t=b is given by $$s = \int^b_a \sqrt{ x'(t)^2 + y'(t)^2 + z'(t)^2 } dt $$ ( this is the integral between $t=a$ and $t=b$ ) ========================================== It is clear that the two points given arise from $t=1$ and $t=2$. since when $t=1$, $r(1) = 1 i + 1 j + 3 k$ which corresponds to $(1,1,3)$ and when $t=2$, $ r(1) = 2 i + 8 j + 6 k$ which corresponds to $(2,8,6)$ For us, $x(t) = t$ $y(t) = t^3$ $z(t) = 3t $ so $x'(t) = 1 $ $y'(t) = 3t^2$ $z'(t) = 3 $ and $s = \int^b_a \sqrt{ 1 + 9t^4 + 9} dt$ $s = \int^b_a \sqrt{ 10 + 9t^4} dt $ when I use the graphic program to approximate this integral I obtain, $s = 7.763$ to 3 decimal places. cheers Jan Hansen