find the max and min values of the function f(x,y,z,t)= (x+y+z+t) subject to the constraint $\displaystyle x^2+y^2+z^2+t^2=49$

I have never calculated for t before and I'm thrown off as how to do it.

You get no critical points from the original equation so I'm assuming it would all be on the boundary. Please help

thank you