jika 12x+3y=9 dan 5x+7y= -2,maka nilai dari 5x + 4y adalah...

12x+3y=9 | x7 | 84x+21y= 63
5x+7y =-2| x3 | 15x+ 21y=-6 (dikurangi)
=> 69x = 69
=> x = 1
x=1 , substitusikan kesalah satu persamaan
x=1 => 5(1)+7y=-2
=> 5+7y = -2
=> 7y = -2-5
=> 7y = -7
=> y = -7/7
=> y = -1
x=1,y=-1 5x+4y=5(1)+4(-1)
= 5-4
= 1