Question

How to do these problems

Answer 1

`\bf \begin{array}{llcll} 3x-y=7&&3x-y=7\\ x+y=-11&\boxed{* -3}\implies &-3x-3y=33\\ &&-------\\ &&0-4y=40 \end{array}\\\\ y=\cfrac{40}{-4}\implies y=-10\\\\ -----------------------------\\\\ \begin{array}{cllll} x-7y=-9\\ -x+8y=10\\ --------\\ 0+y=1 \end{array}\\\\ -----------------------------\\\\ \begin{array}{llcll} 7x+y=14&\boxed{* -3}\implies &-21x-3y=-42\\ 8x+3y=16&&8x+3y=16\\ &&--------\\ &&-13x+0=-26 \end{array} \\\\ x=\cfrac{-26}{-13}\implies x=2`

notice, the 2nd one, had a x and -x, so, we don't have to multiply anything there, just cancel those two out