
PETE C. answered 12/16/19
BS in Mathematics and Certified High School Math Teacher
Since f(-2) = 3, then (-2,3) is one point of the straight line.
And, f(5) = 7 implies (5,7) is another point on the straight line.
A straight line can be defined as : Y = MX + B where M is the SLOPE, or RISE OVER THE RUN,
and B is the Y-INTERCEPT(X is zero). This is named the "SLOPE-INTERCEPT FORMULA".
Let's determine the slope by using the two points from above:
The SLOPE M = RISE/RUN = (7 - 3)/5 - (-2)) = 4/7.
Now, we need to determine the value of B, the Y-INTERCEPT.
Let's use the point (5,7) to plug into the formula Y = MX + B.
7 = ((4/7) * 5) + B
7 = 20/7 + B
7 - (20/7) = B
(49/7) - (20/7) = B
29/7 = B
Since we know the SLOPE is 4/7, and the Y-INTERCEPT is 29/7,
the SLOPE-INTERCEPT FORMULA defining the line is:
Y = (4/7)X + (29/7)
If you wanted to eliminate the fractions, you could multiply the entire equation by 7.
7Y = 4X + 29.
CHECKING:
Does 7Y = 4X + 29?
Use the point (5,7).
7Y = 49
4X + 29 = 20 + 29 = 49
49 = 49