We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.

+0

# Need help, again!

+1
227
2

Please help again!

Find the ordered pair  that satisfies the system of equations

\begin{align*} x+3y &= -4,\\ 3x -7y &= 36. \end{align*}

Nov 10, 2018

### 2+0 Answers

#1
+2

subtract 3x the first equation from the second equation

$$(3x-7y)-3(x+3y) = 36 - 3(-4)\\ -16y=48\\ y=-3\\ \text{use this value of y to obtain x}\\ x + 3(-3) = -4 \\ x - 9 = -4\\ x = 5\\ (x,y) = (5,-3)$$

.
Nov 10, 2018
#2
+2

Substitution: x+3y=-4, so x=-4-3y and 3(-4-3y)-7y=36, -12-9y-7y=36, -9y-7y=48, -16y=48, y=-3. and x=x+3(-3)=-4, x-9=-4, x=5. Thus, the ordered pair is (5, -3).

Elimination: We can also show this by elimination: multiply the first equation by 3, which yields, 3x+9y=-12 and 3x-7y=36. Subtract, 16y=-48, y=-3. Plugging the value of y back in to find the value of x, we get x+3(-3)=-4, x-9=-4, x=5. Thus, the ordered pair is (5, -3).  Nov 11, 2018