Question

explain this..
no spam explanation...of elimination method!!

Answer 1

When you subtract one equation from other, you have to change the signs of the second equation (which is subtracted from the first equation).
You are writing the sign change in between the equations. Write the sign change below second equation.

In case 2, the second equation (which is to be subtracted from the first) is 12x - 9y = - 39.
After sign change, it will be -12x + 9y = 39.
And now you just have to add it.

12x - 12x = 0
20y + 9y = 29y
48 + 39 = 87
So 29y = 87

Remember that, while subtracting, we change the sign. After changing, we just add the equations. and solve.