Question

On the xy plane where $O$ is the origin, given points, $A(1,0),B(0,1)$ and $C(1,1)$. Let $P,Q,R$ be moving points on the line $OA,OB,OC$ respectively such that $\overrightarrow{OP}=45t(\overrightarrow{OA}),\overrightarrow{OQ}=60t(\overrightarrow{OB})$, $\overrightarrow{OR}=(1-t)(\overrightarrow{OC})$ with $t>0$.
If $f(t)=|\overrightarrow{PQ}|$ then the differential coefficient of $f(t)$ when $t=1$, is equal to

• A. 45
• B. 60
• C. 75
• D. 100

Answer 1

Answer: (C)

Correct answer is (c) 75