The resultant of two vectors `vec(P)` and `vec(Q)` is `vec(R)`. If `vec(Q)` is doubled then

The resultant of two vectors `vec(P)` and `vec(Q)` is `vec(R)`. If `vec(Q)` is doubled then the new resultant vector is perpendicular to `vec(P)`. Then magnitude of `vec(R)` is :-

[priyankasinghrajawat]

where is costheta in resultant formula

[ravishankar-pwxn]

Excellent method for solving by dot product

[akankshasingh]

I really don't know how worst is doubtnut such nonsence teachers 😑

[jatinkapil]

Where is costhetaaa??? How do you know the value of thehaa

[fatmanayer]

the whole solution is wrong...u r trying to take out the answer without any cocept..u don't even know the formula & in place of magnitude in the last step u have taken vector...what kind of irony is this..illiterate people

[ranjithpn]

Why didn't you put Q = 2Q in final equation ?

[Funshortsyt]

P + Q =R and P + 2Q = R' well these are vectors not only magnitude, R'dotP = 0 = magnitude RPcosø so pcosø =0 and p = 0, use the main formula and put these values p²+q²+2pqcosø = R², 0 +q²+0=R², R=Q