Big Ideas Math Algebra 1, 2015
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Big Ideas Math Algebra 1, 2015 View details
2. Solving Systems of Linear Equations by Substitution
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Exercise 24 Page 246

Choose arbitrary slopes for each equation and use the point-slope form.

Example Solution: y=2x-55 y=3x-70

Practice makes perfect
We are asked to find a system of equations with (15,- 25) as its solution. For our first equation, we can choose any arbitrary slope and then substitute it, together with x= 15 and y= - 25, in the general formula for the slope-intercept form of a line. Let's choose a slope of 2.
y-y_1=m(x-x_1)
y-( -25)= 2(x- 15)
â–Ľ
Solve for y
y+25=2(x-15)
y+25=2x-30
y=2x-55
We can find the second equation in the same way, as long as we do not choose the same slope! Let's now choose a slope of 3. Again, we know the line passes through ( 15, - 25), and so this becomes our point.
y-y_1=m(x-x_1)
y-( -25)= 3(x- 15)
â–Ľ
Solve for y
y+25=3(x-15)
y+25=3x-45
y=3x-70
When we combine these equations, we form a system of equations which has (15, -25) as its solution. y=2x-55 y=3x-70