1) can't decide what is under the square root, use brackets
the way it stands, dy/dx = 0 + 10cosx
(looks too easy)
2) correct
3) use quotient rule
dy/dx = (8x(cosx) - 8sinx)/(64x^2)
take it from there
More questions on - finding dy/dx
1) y = sqrt 4 + sin 10 x - I am lost again
2) y = 10/sin x
answer: - 10 csc x cot x
3) y = sin x/ 8x
2 answers
y = sqrt (4 + sin 10x)