Jawabanmu

2014-04-09T20:00:08+07:00
aritmatika
a+b =2
a+8b=30
b=4 dan a=-2
S_{20}= \frac{20}{2} (2.a+(20-1)(b))
           = 10(-4+38)
           = 340


Geometri
a r^{2} / a r^{5} = 3/81
 1/r^{3} = 1/27
 r=3 a=1/3
 U_{9} = a r^{8} 
           = 1/3. 3^{8} 
           = 2187