1) 5а^9 - 3а^7 = а^7( 5а^2 - 3 )
2) 4а^8 = а^7 • 4а
3) ( а^7( 5а^2 - 3 ))/( а^7•4а ) = ( 5а^2 - 3 )/4а
16*cos20°*cos40°*cos80°*sin20°=
=8*(2*sin20°*cos20°)*cos40°*cos80°=8*sin(2*20°)*cos40°*cos80°=
=4*(2*sin40°*cos40°)*cos80°=4sin80°*cos80°=2*(2sin80°*cos80°)=2*sin160°
Исходное не пишу
2/(х(х+5))+3/(2(х-5)=15/(х+5)(х-5)
приводим к общему знаменателю 2х(х-5)(х+5)
4х-20+3х²+15х=30х
3х²-11х-20=0
х₁,₂=<u>11⁺₋√(121+240)</u> = <u>11⁺₋19</u>
6 6
х₁=5 х₂=-8/6=-1 1/3