= -28с^2-8c+8+2c=-28c^2-6c+8
5a^4-20a²b+20b²=5*(a²-4a²b+4b²)=5*(a²-2b)²
данo:
<A=35°
<C=70°
AC=27cm
Рассчитываем <B:
<B=180°-(<A+<C)=180°-(35°+70°)=180°-105°=75°
<B=75°
Sin75°=0,9659
Sin70°=0,9397
Sin35°=0,5736
пользуемся формулой синусов:
*AC/sinB=CB/sina=AB=sinC
AC/sin75°=CB/sin 35° to:
27/sin75°=CB/sin35° // *sin35°
CB=27*sin35° /sin75°
CB=27*0,5736 /0,9659=15,4872 / 0,9659=16,0339
CB=16,0330cm
AC/sin75°=AB/sin70° to:
27/sin75°=AB/sin70° // *sin70°
AB=27*sin70°/sin75°
AB=27*0,9397 /0,9659 =25,3719 / 0,9659=26,2676
AB=26,2676cm
St =1/2*AC*AB*sina
St= ½*27*26,2676*0,5736=203,4058cm2
(1+3√5)^2=1+9×5=46
(2√10-√2)^2=4×10-2=38