(x+5)(x-6)(x-17)>0
- + - +
________________-5_____________6____________17___________
x∈(-5;6)∨(17;+∞)
1)хх+2ху+уу=25
хх+уу=21
2) ххх + 3ху(х+у)+ууу=125
ххх+ууу=125-30=95
1206 потомушто 1+2+0+6=9 , а 9:9=1
так что кратно
1.a) =2sin(105°+75°)/2×cos(105°-75°)/2=2sin90°×cos15°=2cos15°
b)= sin(π/2-π/12)+sin7π/12=2sin(π/2-π/12+7π/12)/2×cos(π/2π/127π12) = 2sin0×cos(-π)=0
2/a)=1/2(cos(37°30`-7°30`)-cos(37°30`+7°30`))=1/2(cos30°-cos45°)=1/2(√3/2-√2/2)=
√3/4-√2/4
b)=1/2(cos(75+105)+cos(75-105))=1/2(cos180+cos30)=1/2(-1+√3/2)=-1/2+√3/2