Some Trigonometry problems I need help with...my answers are wrong.?

Ok, what results do you get? Here's 4 problems to start with, I'm using x and y bec I can't put the alpha and Beta character in and in some problems with x it's really theta, for the angle: a) in regards to trigonometric identities-- the expression (1-sin^2x)(1 + tan^2x) b)if cos x=2/5 and sin y = 1, where x is in quad 4 and y is on pos Y axis, then csc (x + y) is equal to what? c) what is the value of tan x/2, if x = 5pi/3 (lesson on half angle formulas) and next problem d)What is the value of sin x/2,when cot x = 5/12, csc x is negative, and x,or the angle, is >0 deg but less than 360deg?