### Home > PC > Chapter 5 > Lesson 5.2.1 > Problem 5-51

5-51.

*u*^{2} − 4*u* = 3*u*^{2}*u*^{3} − 3*u*^{2} − 4*u* = 0*u*(*u*^{2} − 3*u* − 4) = 0*u*(*u* − 4)(*u* + 1) = 0*u* = 0, *u* = 4, *u* = −1

But *u* ≠ 0 because you would have division by zero.

*u* = sin*θ*

−1 = sin*θ*

*u* = sin*θ*

4 = sin*θ*