1) 2^x + 2^(x - 2) < 3
2^x + (!/2)*(2^x) < 3
(2^x) *(3/2) < 3
2^x < 2^1
x < 1
2) 2*sin(π/3) + 2*cos((-π/4)) - 3*tg(π/3) + ctg(π/2) = 2*(√3/2) + 2/(1/√2) - 3*√3 + 0 = √3 + 2/√2 - 3√3 = √2 - 2√3 = (√2 - 2√3)
3) sinα = - 5/13, 3π/2 < α < 2π (4 четверть)<br>cosα = √(1 - sin^2x)
cosα = √[1 - (-5/13)^2] = √[1 - (25/169)] = √(144/169) = 12/13
tgα = sinα/cosα =( -5/13) / (12/13) = - 5/12
ctgα = 1/tgα = - 12/5