1
$\begingroup$
n1 = {6 - 8 m, -2 + 8 m, 4}; n2 = {2, 2, 4};
Solve[VectorAngle[n1, n2] == 150 Degree, m, Reals]

Why can't the equation with the angle between vectors be solved?

enter image description here

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2
  • $\begingroup$ No solution. n1 = {6 - 8 m, -2 + 8 m, 4}; n2 = {2, 2, 4}; Reduce[VectorAngle[n1, n2] == 150 Degree is False $\endgroup$
    – cvgmt
    Commented Aug 24, 2023 at 9:39
  • $\begingroup$ Plot[VectorAngle[n1, n2], {m, -5, 5} , PlotRange -> {{-5, 5}, {-0.2, 3}} , GridLines -> {None, {5 π/6}} , GridLinesStyle -> Directive[Red]] $\endgroup$
    – Syed
    Commented Aug 24, 2023 at 9:40

1 Answer 1

6
$\begingroup$
n1 = {6 - 8 m, -2 + 8 m, 4}; n2 = {2, 2, 4};
FunctionRange[VectorAngle[n1, n2], m, z]

0 <= z < π/2

It means that z=VectorAngle[n1, n2]==150 Degree without solution.

n1 = {6 - 8 m, -2 + 8 m, 4}; n2 = {2, 2, 4};
Reduce[n1 . n2/(Sqrt[n1 . n1] Sqrt[n2 . n2]) == Cos[150 Degree]]

False

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