-5x-7y=5 and -10x-9y=2 if the system is to be solved using the addition method, by what constant should one of the equations be multiplied if the x terms are to drop out?
dont get it!!!!!!!!!!!!1
2007-02-24 11:00:27 · 8 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
You're blocking yourself. What do you multiply -5x by so that when you add -10x to the result, you get 0? Well, -10x + 10x = 0, so multiply -5x by -2 to get 10x. -2 is your answer. See how it works:
-2[ -5x - 7y = 5]
-10x - 9y = 2
10x + 14y = -10
-10x - 9y = 2
-----------------------
0 ......+5y = -8
y = -8/5
by eliminating the x's you can get y.
2007-02-24 11:08:53 · answer #1 · answered by Philo 7 · 0⤊ 0⤋
Okay, you want to add a multiple of one equation to another, like so:
k*(-5x-7y=5) + (-10x-9y=2)
The problem is asking you what value must k have so that when you do this, the x terms will cancel. Ignore the rest of the problem and just think about the coefficients of the x term for a moment. When you add them you will get:
k*(-5)x + (-10)x + y-terms = constant
So, what does k have to be so that k*(-5)x + (-10)x = 0? Obviously, it should be -2. In general, given an equation of the form:
ax+by=c
dx+ey=f
You may eliminate the x-terms by multiplying the first equation by -d/a and adding it to the second. This is not the only way of course -- you could also multiply the second equation by -a/d and add it to the first. Which is easiest will depend on the particular coefficients you are given.
2007-02-24 19:09:31 · answer #2 · answered by Pascal 7 · 0⤊ 0⤋
-5x-7y=5
-10x-9y=2
you're going to add them currently if you add you get
-15x-14y=7
The question wants to know what you need to multiply by either equation to have a result of 0x + somey = something when you add vertically
So to get the x's to cancel out you need to multiply so the x coefficients are the same, except different signs. so if you multiply the top equations by -2, -5*-2 = 10x and the x terms drop out when added
-2
2007-02-24 19:05:26 · answer #3 · answered by radne0 5 · 0⤊ 0⤋
Multiply 1st equation by -2 getting 10x +14y =-10.
Now when you add this new equation to the 2nd equation, the x term ix eliminated.
2007-02-24 19:06:39 · answer #4 · answered by ironduke8159 7 · 0⤊ 0⤋
multiply the first by -2 and the equation becomes
10x+14y=-10
add to the second to get
5y=-8 or y=-8/5
2007-02-24 19:05:58 · answer #5 · answered by Rob M 4 · 0⤊ 0⤋
Multiply the first set by -2. Then you get 10x+14y=-10. Finnish it yourself so you can learn.
2007-02-24 19:18:25 · answer #6 · answered by Toeless_Joe_Jackson 5 · 0⤊ 0⤋
The first equation should be multiplied by 2.
2007-02-24 19:06:27 · answer #7 · answered by bruinfan 7 · 0⤊ 0⤋
(-5x-7y=5 (-2)
(-10x-9y=2
(10x +14y = -10
(-10x -9y = 2
5y = -8
y = -8/5
y = -1,6
-10x - 9(-1,6) = 2
-10x = 2 - 14,4
x = -12,4 : -10
x = 1,24
2007-02-24 19:36:22 · answer #8 · answered by aeiou 7 · 0⤊ 0⤋