Question 58·Easy·Nonlinear Functions
What is ?
For function-evaluation questions, substitute the given -value carefully into the function, watching parentheses and negative signs. If the expression is a rational function with a factorable quadratic, consider factoring and canceling common factors first (making sure the denominator is not zero) to turn the problem into a simple linear evaluation. When you finish, quickly estimate the sign and rough size of your answer to catch common arithmetic mistakes before choosing from the options.
Hints
Start with substitution
To find , think about what happens if you replace every in with . Write out the new numerator and denominator separately before simplifying.
Consider simplifying first
Before plugging in , see if you can factor the numerator and cancel any common factors with the denominator (as long as the denominator is not zero).
Be careful with signs
When you compute the numerator after substitution or after simplifying, pay close attention to negative signs: subtracting a negative and dividing by a negative can change the sign of the final result.
Check with a different method
If you evaluate directly from the original fraction, try also evaluating it from a simplified form of and make sure both approaches give the same value.
Desmos Guide
Evaluate directly in Desmos
In a new expression line, type (2^2 - 3*2 - 10)/(2 - 5) exactly as the function definition with . Desmos will show a single numeric output to the right; that value is .
Optional: Simplify first, then evaluate
In one line, type (x^2 - 3x - 10)/(x - 5) and let Desmos graph it. In a second line, type y = x + 2. Notice that the graphs overlap except at . Now either:
- Add a table to the first expression and enter
2in the -column, or - Type
2 + 2in a new line. The resulting numeric output is the value of .
Step-by-step Explanation
Understand what means
The question is asking you to evaluate the function at .
That means you should replace every in
with and simplify, or simplify the function first and then substitute .
Simplify the function by factoring
Factor the quadratic in the numerator:
So for ,
Now cancel the common factor in the numerator and denominator (this is allowed as long as ):
Substitute into the simplified expression
Now use the simplified form for .
Substitute :
Compute the final value and match the choice
Evaluate the sum:
So , which corresponds to choice D.