Question

1.If a line with a slope of -3 crosses the y-axis at (0,7), what is the equation of the line?

Answer 1

y = mx + b    "m" is the slope, "b" is the y-intercept (the y value when x = 0)

1. slope: -3

y-intercept: 7

y = -3x + 7

Your answer is B

y + 3x = 7   Subtract 3x on both sides

y = -3x + 7

2. y + 9(x + 3) = 0     Multiply/distribute 9 into (x + 3)

y + 9x + 27 = 0      Subtract 9x and 27 on both sides to get "y" by itself

y = -9x - 27

slope: -9

y-intercept: -27 or (0,-27)

Your answer is D

3. Point-slope form:   y - y₁ = m(x - x₁)

slope: -11

(x₁ , y₁) = (-5, 7)

y - 7 = -11(x - (-5))  The two negative signs becomes a positive

y - 7 = -11(x + 5)

Your answer is C

4. For this question, I think you get it from point-slope form to slope-intercept form (I'm not sure, but you still get the same answer if you just do slope-intercept form)

slope: -4

(x₁ , y₁) = (2, -8)

y - y₁ = m(x - x₁)

y - (-8) = -4(x - 2)

y + 8 = -4(x - 2)     Multiply/distribute -4 into (x - 2)

y + 8 = -4x + 8       Subtract 8 on both sides to get "y" by itself

y = -4x

Your answer is A