4) t=√[a(a+2)(a+4)(a+6)+16]
notam b=a+3
=> a(a+2)(a+4)(a+6)=(b-3)(b-1)(b+1)(b+3)
=(b²-1)(b²-9)
=b^4-10b²+9
=> t=√( b^4-10b²+9+16)
t=√( b^4-10b²+25)= =√( b²-5)²
t= b²-5 ; t=(a+3)²-5
t=a²+6a+9-5
t=a²+6a+4; t∈Q
5 )m(<BAC)=90; AC=6 cm; ctg(<ACB)=1/7
a) ctg(<ACB)=AC/AB=1/7
=> AB=7AC=42 cm
BC²= AB²+ AC²=(1764+36)cm²=1800cm²
BC=30√2 cm
b) A ΔABC=AB•AC/2=42cm•6cm/2=126cm²
