JEE Previous Year Question

Let three vectors $a\text{,}b$and $c$ be such that $c$ is coplanar with $a$ and $b\text{,}a\cdot c=7$ and $b$is perpendicular to $c$where $a=-i+j+k$and $b=2i+k$ then the value of $2\text{|}a+b+c{\text{|}}^2$ is

Topic: JEE PYQ

Answer: 75. Full step-by-step solution below.