Question

Solve the simultaneous equations:
4x+7y=1
3x+10y=15

Answer 1

`\left \{ {*(-3) \atop *4} \right. \\\\ \left \{ {{-12x-21y=-3} \atop {12x+40y=60}} \right. \\+-----\\Addition\ method\\\\\ -21y+40y=-3+60\\19y=57\ \ |:19\\\\y=3\\4x=1-7y\\x=(1-7y)/(4)\\x=(1-7*3)/(4)=(-20)/(4)=-5\\\\ Solution:\\ x=-5\\y=3`

Answer 2

Ok we need a common coefficient of either x or y:
12x+21y=3
12x+40y=60
We can subtract one from the other to get:
19y=57
Now divide by 19 to get:
y=3
Now if we sub this back in we see that:
3x+30=15
3x=-15
x=-5