Если я не допустил ошибки то получается так
Ответ:
Объяснение:
а)2а²-3а+1-7a²+5a=-5a²+2a+1
б) 3х(4х²-х)=12х³-3х²
в)(х-8)(х+5)=х²-8х+5х-40=х²-3х-40
г) (х+6)²=х²+12х+36
sin10sin30sin50sin70=cos10sin10sin30sin50sin70/cos10=
=1/2sin20sin70sin30sin50/cos10=1/4sin40sin50sin30/cos10=
=1/8sin80sin30/cos10=1/8cos10sin30/cos10=
=1/8sin30=1/8*1/2=1/16=0.0625
или
sin10sin30sin50sin70=1/2sin10sin50sin70=
=1/4(cos40-cos60 )sin70=1/4(cos40-0.5)sin70=
=1/4cos40sin70-1/8sin70=1/8(sin110+sin30)-1/8sin70=
=1/8sin110+1/16-1/8sin70=1/8sin(180-70)+1/16-1/8sin70=
=1/8sin70+1/16-1/8sin70=1/16=0.0625