1. (tg(π/2-α)-ctg(π/2+α))²=(ctgα-(-tgα))²=(ctgα+tgα)².
2. (ctg(π+α)+ctg(3π/2+α))²=(ctgα+(-tgα))²=(ctgα-tgα)².
3. (ctgα+tgα)²-(ctgα-tgα)²=(ctgα+tgα+ctgα-tgα)*(ctgα+tgα-(ctgα-tgα)=
=(ctgα+tgα+ctgα-tgα)*(ctgα+tgα-ctgα+tgα)=2*ctgα*2*tgα=4*1=4.
(2-x)/x≥0
1-x≥0
x∈(0;2]
x∈(-∞;1]
Ответ: x∈(0;1]
7x-11>=10x-8; 7x-10x>= -8+11; -3x>=3; x<= -1. Ответ: x<= -1.