"Let $T$ be the smallest positive real number such that the tangent to the helix $(\cos t)i + (\sin t)j + (t/(2^{1/2}))k$ at $t=T$ is orthogonal to the tangent at $t=0$ . Then $F = (x)j - (y)i$ along the section of the helix from $t = 0$ to $t = T$ is $2$ .
How ? Here $i$,$j$,$k$ are the three unit vectors along $x$,$y$,$z$-axes , respectively" . Please help with this problem...I have simply evaluated the line integral to be $T$...but the answer is $2$...I think the orthogonality has some role in it...but I don't understand how...I have just begun vector calculus !