If the system (6x - 6y = 7 and 18x - 5y = 6 ) is to be solved using the addition method, by what constant?

Question

should one of the equations be multiplied if the x terms are to drop out?

Choices:
a) 6
b) 1/3
c) -3
d) -6

Answer 1

6x - 6y = 7 ........(1)
18x - 5y = 6 ........(2)

You want to make the coefficients of the x terms numerically equal, so that when you add or subtract the equations x will disappear.
From the options you are given, I would choose (c) -3.
Multiply (1) by -3:
-18x + 18y = -21 .......(3)
Now, when you add (1) and (3), x disappears.

Answer 2

on scratch paper, divide the X coefficients by each other [do this twice, once for each equation]; remember the answer after you add the equations needs to be zero X.

details are left to the student.


:-)

Answer 3

d) -6.