Tolong dijawab secepatnya....nanti dikumpul

a+b =akar a^2+b^2+2ab+cos90
= akar 2^2+3^2+2.2.3+0
= akar 4+9+12
= akar 25
= 5
a+b+c = akar a^2+b^2+2ab+cos90+c^2+2bc+cos90 = akar 2^2+3^2+2.2.3+0+4^2+2.4.3+0 = akar 4+9+12+16+24 = akar 65
(a+b).(a+b+c) = 5.akar 65 = 5akar65