Answer:
a) dE={KdQdX}{r^{2} } *cosT
b) E = (2Q)/4eL^2)
Step-by-step explanation:
a) The charge of element is:
dQ = Q/L
Where the y-axis elements will cancel, thus:

where dX is the length element = RdT and dT is the angle element, K = 1/(4pe)
b) The angle from x-axis is:

We integrate the expression from T to p/2 and multiply by 2:

Replacing the k value:
