Dr. J's Maths.com
Where the techniques of Maths
are explained in simple terms.

Exponential functions - Basic understanding.
Test Yourself 1 - Solutions.


 

 

Basic manipulation. 1. Simplify (7x)4 - 34.

2. Simplify .

  3. Expand .

22y - 2×2yex + e2x

= 4y - 2y+1ex + e2x

4. Simplify (2 × 3x)×(3 × 2x)

6 × 3x2x = 6×(3×2)x

= 6x+1

  5. 6. For f(x) = 2ex + 3e2x- 1, evaluate

f(2) - f(0) =

(2e2 + 3e4 - 1) - (2 + 3 - 1)

=2e2 + 3e4 - 5

Graphs. 7.

Both growth curves:

  • pass through (0, 1);
  • y = 3x climbs less slowly and is below y = 5x for x > 0;
  • y = 3x falls slower and is therefore above y = 5x for x < 0.
8.

The basic exponential growth curve
(y = ex) rises as x increases.

The transformation of "+ 3" moves the curve up so that now it has y = 3 as its asymptote rather than the x-axis.

The y intercept is at y = e 0 + 3 = 4.
At x = 1, y = 3 + e = 3 + 2.7 = 5.7.

  9.

The negative sign in front of the exponential term turns the graph of the decay curve upside down.

The addition transformation of +3 moves the curve up 3 units so the asymptote rises from y = 0 to y = 3.

The coefficient and index both of 2 make the curve fall more rapidly.

10. .

The basic exponential growth curve
(y = -e-x) rises as x increases.

The addition transformation of +1 moves the curve up 1 unit so the asymptote rises from y = 0 to y = 1.

The coefficient of 2 makes the curve rise more quickly as x increases.

  11.

The catenary adds both exponential functions together. Hence the y intercept equals (1 + 1)÷ 2 = 1.

The addition also means that the curve on both sides of the y axis has a larger y value than each of the two basic exponential curves.

Clearly also the function is even.

12.

At the intersection of the two curves, the y values are the same. Hence we replace the exponential function in the combined equation and put the equation - 0 as there is no difference between the y values.

f(x) = e-x - x + 1 = y - x + 1 = 0

So we obtain y = x - 1

As there is only one point of intersection, the combined equations have exactly one root.

  13. 14.
  15. 16.