Question

Use the substitution method to solve the system of equations. Choose the

correct ordered pair,
16-2y=74
2x-2y=4

Answer 1

(1) x= 5, y = 3

(2) x = -27, y = -29

Explanation:

If the frist equation is 16x - 2y = 74

`\\\\\left\{\begin{array}{ccc}8x-y=37\\x-y=2&\text{add y to both sides}\end{array}\right\\\\\left\{\begin{array}{ccc}8x-y=37&(1)\\x=2+y&(2)\end{array}\right\\\\\\\text{substitute (2) to (1):}\\\\8(2+y)-y=37\qquad\text{use the distributive property:}\ a(b+c)=ab+ac\\16+8y-y=37\qquad\text{subtract 16 from both sides}\\7y=21\qquad\text{divide both sides by 7}\\\boxed{y=3}`

`\text{put the value of y to (2):}\\\\x=3+2\\\boxed{x=5}`

If the first equation is 16 - 2y = 74

`\left\{\begin{array}{ccc}16-2y=74&\text{divide both sides by 2}\\2-2y=4&\text{divide both sides by 2}\end{array}\right\\\left\{\begin{array}{ccc}8-y=37&\text{subtract 8 from both sides}\\x-y=2\end{array}\right\\\left\{\begin{array}{ccc}-y=29&\text{change the signs}\\x-y=2\end{array}\right\\\left\{\begin{array}{ccc}y=-29&\text{put it to the second equation}\\x-y=2\end{array}\right\\\left\{\begin{array}{ccc}y=-29\\x-(-29)=2\end{array}\right\\\left\{\begin{array}{ccc}y=-29\\x+29=2&\text{subtract 29 from both sides}\end{array}\right`

`\left\{\begin{array}{ccc}y=-29\\x=-27\end{array}\right`