The 7th term in  1y+y210,when expanded in descending power of y, is

When 1y+y210is expanded, the powers of y go on increasing as the terms proceed. Hence it is expanded in ascending powers of y. So y2+1y10,when expanded, will be in descending powers of y.Hence t7=10C6(y2)4(1y)6=10×9×8×74×3×2×1y2=210y2