Jawabanmu

2014-03-10T21:47:16+07:00
U3 = a +(3-1)d = 10
     = a + 2d    = 10
u7 = a + (7-1)d = 22
    = a + 6d = 22
kurangkan yg di bold
-4d = -12
d = 3 ,sub ke a + 2d = 10
a+ 2.3 = 10
a + 6 = 10
a = 4

Sn = n{2a+(n-1)d}
               2
S30 = 30 {2.4 + (30-1)3}
                  2
= 15 ( 8 +29.3)
=15.95 = 1425


2014-03-10T21:50:10+07:00
* 10 = a + 2b            * a+2b = 10
   22 =a+ 6b  _            a+2 . 3 = 10
   -12 = - 4b                a + 6   = 10  
   -12/-4 = b                    a    = 10 - 6 = 4
       3    = b

*Sn = n/2(2a+(n-1)b)
 S30 = 30/2 (2.4 + (30 -1 ) 3)
        = 15 ( 8 + 29 . 3)
        = 15 . 95 = 1425