AP Exam KitAP Precalculus
Unit 22.13 Exponential and Logarithmic Equations and InequalitiesCalculator required

To the nearest hundredth, what is the positive solution of 2.4x=7x2.4^x=7-x?

Original exponential-line intersection sketchAn increasing exponential curve and a decreasing line cross once between x=1 and x=2.xy
An increasing exponential curve and a decreasing line cross once between x=1 and x=2.
  1. x=1.36x=1.36
  2. x=1.58x=1.58
  3. x=1.87x=1.87
  4. x=2.40x=2.40

Answer and derivation

Correct answer: C

The graphs intersect at approximately x=1.87x=1.87.

  1. Enter both sides as separate functions.
  2. Locate the only crossing in the positive window.
  3. The x-coordinate is about 1.8681.868, which rounds to 1.871.87.

Why the other options fail

A
This results from an early rough visual estimate.
B
This can result from using an inaccurate table step.
C
Correct numerical intersection and rounding.
D
It copies the exponential base.

Common misconception: A graphing result should identify the equation and report the requested coordinate and precision.

China/AP bridge: China-course bridge: numerical equation solving extends graph intersections; AP expects technology use plus written equation and precision; unlike relying on pixel reading, use the intersect feature; avoid typing multiplication in place of exponentiation.

Original author: AP Exam KitMathematical review: REV-2D-08