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  1. Home
  2. 12th grade
  3. Precalculus
  4. Exercise : Solve equations with radical functions

Solve equations with radical functions Precalculus

Solve the following equations.

\left(2x+3\right)^{-1/2} = 2

Raise both sides to the \left(-2\right) power:

\left( \left(2x+3\right)^{-\frac{1}{2}} \right)^{-2}=2^{-2}

Which is equivalent to:

2x+3=\dfrac{1}{4}

2x=-\dfrac{11}{4}

x=-\dfrac{11}{8}

The solution of the equation is x=-\dfrac{11}{8}.

\left(4x-3\right)^{-1/4} = 5

Raise both sides to the \left(-4\right) power:

\left( \left(4x-3\right)^{-\frac{1}{4}} \right)^{-4}=5^{-4}

Which is equivalent to:

4x-3=\dfrac{1}{625}

4x=\dfrac{1\ 876}{625}

x=\dfrac{469}{625}.

The solution of the equation is x=\dfrac{469}{625}.

\left(5x+8\right)^{-2/3} = 4

Raise both sides to the \left( -\dfrac{3}{2} \right) power:

\left( \left(5x+8\right)^{-\frac{2}{3}} \right)^{-\frac{3}{2}}=4^{-\frac{3}{2}}

Which is equivalent to:

5x+8=\dfrac{1}{8}

5x=-\dfrac{63}{8}

x=-\dfrac{63}{40}.

The solution of the equation is x=-\dfrac{63}{40}.

\left(3x-5\right)^{1/2} = 7

Raise both sides to the second power:

\left( \left(3x-5\right)^{\frac{1}{2}} \right)^{2}=7^{2}

Which is equivalent to:

3x-5=49

3x=54

x=18.

The solution of the equation is x=18.

\sqrt{2x^{2}+5x-3}=x-3

Raise both sides to the second power:

\left( \sqrt{2x^{2}+5x-3} \right)^{2}=\left(x-3\right)^{2}

Which is equivalent to:

2x^{2}+5x-3=x^{2}-6x+9

x^{2}+11x-12=0

Apply the quadratic formula:

x=\dfrac{-11-\sqrt{\left(11\right)^{2}-4\left(1\right)\left(-12\right)}}{2\left(1\right)}=\dfrac{-11-\sqrt{169}}{2}=-12

Or

x=\dfrac{-11+\sqrt{\left(11\right)^{2}-4\left(1\right)\left(-12\right)}}{2\left(1\right)}=\dfrac{-11+\sqrt{169}}{2}=1

Test if any of the solutions are extraneous by plugging them into the initial equation:

\sqrt{2\left(-12\right)^{2}+5\left(-12\right)-3}=\left(-12\right)-3

\sqrt{225}=-15 which is not true, so x=-12 is an extraneous solution.

\sqrt{2\left(1\right)^{2}+5\left(1\right)-3}=1-3

\sqrt{4}=-2 which is not true, so x=1 is an extraneous solution as well.

The equation \sqrt{2x^{2}+5x-3}=x-3 has no solution.

\sqrt{x^{2}+11x-3}=x-4

Raise both sides to the second power:

\left( \sqrt{x^{2}+11x-3} \right)^{2}=\left(x-4\right)^{2}

Which is equivalent to:

x^{2}+11x-3=x^{2}-8x+16

19x=19

x=1

Test if the solution is extraneous by plugging it in the initial equation:

\sqrt{\left(1\right)^{2}+11\left(1\right)-3}=\left(1\right)-4

\sqrt{9}=-3 which is not true, so x=1 is an extraneous solution.

The equation \sqrt{x^{2}+11x-3}=x-4 has no solution.

\sqrt{13x+43}=x+5

Raise both sides to the second power:

\left( \sqrt{13x+43} \right)^{2}=\left(x+5\right)^{2}

Which is equivalent to:

13x+43=x^{2}+10x+25

x^{2}-3x-18=0

Apply the quadratic formula:

x=\dfrac{-\left(-3\right)-\sqrt{\left(-3\right)^{2}-4\left(1\right)\left(-18\right)}}{2\left(1\right)}=\dfrac{3-\sqrt{81}}{2}=-3

Or

x=\dfrac{-\left(-3\right)+\sqrt{\left(-3\right)^{2}-4\left(1\right)\left(-18\right)}}{2\left(1\right)}=\dfrac{3+\sqrt{81}}{2}=6

Test if any of the solutions are extraneous by plugging them in the initial equation:

\sqrt{13\left(-3\right)+43}=\left(-3\right)+5

\sqrt{4}=2 which is true, so x=-3 is a viable solution.

\sqrt{13\left(6\right)+43}=\left(6\right)+5

\sqrt{121}=11 which is true, so x=6 is a viable solution as well.

The solutions of the equation \sqrt{13x+43}=x+5 are x=-3 and x=6.

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See also
  • Course : Radical functions, roots and rational exponents
  • Exercise : Simplify expressions involving exponents
  • Exercise : Determine the domain of radical functions or functions with rational exponents
  • Exercise : Determine the growth or decay of a function with a rational exponent
  • Exercise : Solve inequalities with radical functions
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