nilai x yang memenuhi sistem persamaan 1+3x = -4y dan 9x = 2y+4 adalah a. 1/2 b. 1/3 c. -1/3 d. -1/2

1 + 3x = -4y <-----> 3x = -4y -1  (i)
9x = 2y+ 4 ..........(ii)
eliminasi y
3x = -4y - 1 |*1| 3x = -4y -1
9x = 2y+ 4 |*2| 18x = 4y + 8
                         -----------------  +
                          21 x = 7
                               x = 7/21
                               x = 1/3 ................(B)

1+3x=-4y ⇔3x=-4y-1⇔*1⇔3x=-4y-1
                   9x=2y+4⇔*2⇔18x=4y+8
                                                -
                                         ⇔21x=7
                                         ⇔x=7/21
                                              =1/3(b)