Осталось 4 куска.Так как 1) 5+7=12 2)12-8=4-осталось всего!
Ответ:63•4=252
ОТВЕТ-у старших школьников 252 наименования книг.
Х2+2х-15=0
Л=4+60=64=8
х=-2-8/2=-5
х=-2+8/2=3
х2+7х-18=0
Д=49+72=121=11
х=-7-11/2=-9
х=-7+11/2=2
3х2+4х-7=0
Д=16+84=100=10
х=-4-10/6=-2,3
х=-4+10/6=1
2у2-7у-9=0
Д=49+72=121=11
у=7-11/4=-1
у=7+11/4=4,5
(1-сos4x)²/4+(1+cos4x)²/4=5/8
2-4cos4x+2cos²4x+2+4cos4x+2cos²4x=5
4cos²4x=1
4(1+cos8x)/2=1
2+2cos8x=1
2cos8x=-1
cos8x=-1/2
8x=-2π/3+2πk U 8x=2π/3+2πk
x=-π/12+πk/4 U x=π/12+πk/4,k∈z
0≤-π/12+πk/4≤π U 0≤π/12+πk/4≤π
0≤-1+3k≤12 U 0≤1+3k≤12
1≤3k≤13 U -1≤3k≤11
1/3≤k≤13/3
k=1⇒x=-π/12+π/4=π/6
k=2⇒x=-π/12+π/2=5π/12
k=3⇒x=-π/12+3π/4=2π/3
k=4⇒x=-π/12+π=11π/12
0≤-1+3k≤12 U 0≤1+3k≤12
-1≤3k≤11
-1/3≤k≤11/3
k=0⇒x=π/12
k=1⇒π/12+π/4=π/3
k=2⇒x=π/12+π/2=7π/12
k=3⇒x=π/12+3π/4=5π/6