1) 0,81x-71=1,11х+1
0,81х-1,11=1+71
-0,3х=72
х= 72:(-0,3)
х=-240
2) 4(х+3)=5(х-2)
4х+12=5х-10
4х-5х=-10-12
-1х=-22
х=22
3) 3(х-5)-2(х+4)=-5х+1
3х-15-2х+(-8)=-5х+1
3х-2х+5х=1+15-(-8)
6х=24
х=4
(2x+3)/(x²+x-12)-1/2≤0
(4x+6-x²-x+12)/(x²+x-12)≤0
(-x²+3x+18)/(x²+x-12)≤0
(x²-3x-18)/(x²+x-12)≤0
(x-6)(x+3)/(x+4)(x-3)≤0
x=6 x=-3 x=-4 x=3
+ _ + _ +
------(-4)--------[-3]---------(3)--------[6]-------
x∈(-4;-3] U (3;6]
(sin4a+sin5a+sin6a)/(cos4a+cos5a+cos6a)=
=(2sin((4a+6a)/2)*cos((6a-4a)/2)+sin5a)/(2cos((4a+6a)/2)*cos((6a-4a)/2)+cos5a)=
=(2sin5a*cosa+sin5a)/(2cos5a*cosa+cos5a)=
=(sin5a(2cosa+1))/(cos5a(2cosa+1))=sin5a/cos5a=tg5a