Day 5 Objective – Students should be able to: Find the y intercept when given the slope and a point on the line.

Find the equation To find the equation we need Slope (given) Y – intercept So far we have this much of our equation— y=2x + b We need to find the “b” The slope of a line is 2 A point on the line is (2,5)

The Steps The slope of a line is 2 A point on the line is (2,5) y = 2x + b 5 = 2(2) + b 5 = 4 + b -4=-4 1 = b 1)Fill in the given Slope. 2)Substitute the given point for x and y. 3)Solve for b 4)Fill in the y intercept in your equation. y = 2x + 1

Try One Find the equation of a line that passes through the point (-2, 4) and has a slope of 4. We know this much y = 4x + b Substitute the points (-2, 4) for x and y. Be CAREFUL not to switch them. This is a common error.

Substitute and Solve We know… y = 4x + b the point (-2, 4) is on the line. 4 = 4(-2) + b 4 = -8 + b +8 = = b Complete Equation is y = 4x + 12

Practice Given - Point on the line is (-3, -1) Slope is 3 y = 3x + b -1 = 3(-3) + b -1 = -9 + b +9 = +9 8 = b y = 3x + 8

Practice Given - Point on the line is (6, 8) Slope is 1/2 8 = ½(6) + b 8 = 3 + b -3=-3 5 = b y = 1/2 x + b y = ½ x + 5

Practice Given - Point on the line is (12, 48) Slope is 1/4 y = ¼ x + b 48 = ¼ (12) + b 48 = 3 + b -3 = = b Y = ¼ x + 45

What if you just have a line? If you have a line, you can find the equation. 1)Find the slope of the line using 2 points and the slope formula. 2)Use one point and the slope you just found to find the y - intercept. Now you have all you need for the equation!

Try One First find slope (6, 0) and (0, -4) y = 2/3x + b 0 = 2/3(6) + b 0 = 4 + b -4 = = b y = 2/3x - 4

Practice – Find the Equation Find the equation of the line that passes through (3,6) and (-2, 5). First the Slope using the slope formula Then put the slope in the equation Substitute one of the points for x and y Solve for b

Practice Your teacher will give you 2 points Find the equation