There are 4 positive integers a, b,c, d, such that 4cos(x)cos(2x)cos(4x) = cos(ax)+cos(bx)+cos(cx)+cos(dx) for all values of x. find a+b+c+d.?

At a constant it will take one hour to travel 32 mi.at that speed it will take 1/2 hr to travel the remaining 16 mi.it will take 1+1/2 hr to travel the 48mi @ 32mph.so 1 hr = 60 min& 1/2 hr = 30 min1+1/2 hr = 90 min.there are 60s in each 90 × 60 = 3600 seconds.the real question seriously is he why are they driving so slow? ! lol.