What is the phase constant? Use a cosine function to describe the simple harmonic motion. http://capa.physics.mcmaster.ca/figures/kn/Graph14/kn-pic1416_new.png [Broken] t1=40.0 s and A=20.0 cm I'm really lost on how to get this done. Using x=Acos(ωt+φ); my approach has been to find when cos()=1 or 0 and then setting the phase equal to either 0 or pi/2 respectively. So far, I have ω=pi/10 rad and I know pi<φ<3pi/2. I'm stuck past this though (didn't get very far)...I tried it assuming the graph was accurate in scale and that it was 225deg (5pi/4 rad) but it was incorrect. I've also tried -10=20cos((pi/10)0+φ) --> φ=120deg; then adding a fraction of the period to get it in the proper phase, getting 240deg or 210deg (tried all, incorrect). I am sure there is a more mathematical way to do it, that I am just missing or that I am starting, but not finishing correctly. Any help would be appreciated. Thanks!