I'm reading "Robot Modeling and Control" by Spong. It seems to me there are mistakes in the manual solutions provided by the authors. I came across the following two questions
In this answer I think there is no $d_3$. It should be zero. In the following question
In my solution $\alpha_2=-90^\circ$ not $90^\circ$ and $\theta_3 = 0^\circ$ not $-90^\circ$. I would love to hear your feedback. Also, if you are instructor, you may need to double check this.