Question 105·Hard·Linear Functions
A drone’s dashboard displays a “battery reading” after the drone has flown miles. The drone’s actual battery percentage is linear, and the display is related to the actual battery by
During one flight, the display shows and .
Which choice is the equation of ?
When a linear function is transformed into another linear function (here, becomes via scaling and shifting), find the simpler/observable function first using two points. Then algebraically undo the transformation step-by-step (undo shifts, then undo scaling) to recover the original linear function.
Hints
Write an equation for the display function
Use the two given values and as points to find the slope and intercept of the linear function .
Isolate
From , add 5 to both sides and then multiply by the reciprocal of .
Substitute and simplify carefully
After you get in terms of , substitute your expression for and combine constants using a common denominator.
Desmos Guide
Define the two display points
In Desmos, enter points and .
Create the display line
Compute and , then enter .
Convert to the actual battery function
Enter and simplify the expression Desmos shows.
Match to an answer choice
Compare the simplified form of to the four options and select the exact match.
Step-by-step Explanation
Find the linear function from two points
The points on the line are and .
Slope:
Use to find in :
So
Solve the display relationship for
Given
add 5 to both sides and multiply by :
Substitute and simplify
Substitute :
Distribute and state the equation
Therefore, .