x+x+x-1.4=13
3x=14.4
x=4.8-это стороны , 13-(4,8*2)=3,4см-осн.
(5a+0.4)^2=25a^2+4a+1.6
(2x-1)(4x^2+2x+1)=2x^3+2x^2+2x-4x^2-2x-1=2x^3-2x^2-1
sin20+cos20=sin20+sin70=2sin((20+70)/2)cos((70-20)/2)=2sin45cos25