1/2cos2x+1/2cos4x-cos2x=0
1/2cos4x-1/2cos2x=0
1/2*(2cos²2x-1)-1/2cos2x=0
cos²2x-1/2cos2x-1/2=0
cos2x=a
a²-0,5a-0,5a=0
D=0,25+2=2,25
a1=(0,5-1,5)/2=-0,5⇒cos2x=-0,5⇒2x=+-5π/6+2πn⇒x=+-5π/12+πn
a2=(0,5+1,5)/2=1⇒cos2x=1⇒2x=2πn⇒x=πn
1) a3=a1+2d=a1+6
a1+6=10
a1=4
a8=4+3×7=25
2) a3=a1+2d=a1+2
a1+2=10
a1=8
a6=8+1×5=13
3) a11=12-4×10=-28
4) a9=a1+16
a1+16=11
a1=-5
S12=(2a1+d (n-1))/2 ×n=( -10+22)/2 ×12=72
1)180*0.2=36(г)-яблок
<span>2)180-36=144(г)-масса смеси</span>
1)a1q-a1=-4⇒a1(q-1)=-4⇒a1=-4/(q-1))
a1q²-a1=8⇒a1(q²-1)=8⇒a1=8/(q²-1)
-4/(q-1)=8/(q-1)(q+1)
q+1=-2
q=-3
a1=-4/(-3-1)=1
1;--3;9;-27;...
2)a1+a1q³=0,4375⇒a1(1+q³)=0,4375
a1q²-a1q+a1=0,875⇒a1(q²-q+1)=0,875
a1(1+q)(1-q+q²)=0,4375
(1+q)*0,875=0,4375
1+q=0,4375:0,875
1+q=0,5
q=-0,5
a1=0,4375:(1-0,125)
a1=0,4375:0,875
a1=0,5
0,5;-0,25;0,125;...