Solving Equations with Radicals and Exponents
Raising Each Side to a Power
Example 1
Raising each side to a power to eliminate radicals
Solve each equation.
a)
b)
a)
|
|
Original equation |
|
|
Cube each side. |
3x + 5 |
= x - 1 |
|
2x |
= -6 |
|
x |
= -3 |
|
Check x = -3 in the original equation:
Note that
is a real number. The solution set is
{-3}. In this example we
checked for arithmetic mistakes. There was no possibility of extraneous solutions
here because we raised each side to an odd power.
b)
|
= x |
|
|
|
Original equation |
3x + 18 |
= x2 |
|
|
|
Square both sides. |
-x2 + 3x + 18 |
= x2 |
|
|
|
Simplify. |
x2 - 3x - 18 |
= 0 |
|
|
|
Subtract x2 from each side
to get zero on one side. |
(x - 6)(x + 3) |
= 0 |
|
|
|
Multiply each side by -1 for easier factoring. |
x - 6 |
= 0 |
|
|
|
Factor. |
x |
= 0 |
or |
x + 3 |
= 0 |
Zero factor property |
|
= 6 |
or |
x |
= -3 |
|
Because we squared both sides, we must check for extraneous solutions. If x
= -3
in the original equation
, we get
which is not correct. If x = 6 in the original equation, we get
which is correct. The solution set is
{6}.
|