I have the following equation $\displaystyle y=-20cos225t+50$ If i set y= 60 and i solve i get root 2 over 2, howevef if i sub that back in the equation, i don't get 60 but I get about 68! Any help is appreciated. Here is what i did:

$\displaystyle 60=-20cos225t+50$

$\displaystyle t=10/-20cos225$

$\displaystyle t= root 2/2$